Creep-resistant magnesium alloy

FIELD: metallurgy; production of magnesium alloys which are creep-resistant at high temperatures.

SUBSTANCE: magnesium-based alloys are used for manufacture of articles and castings, cylinder blocks for example. Proposed alloy contains neodymium, cerium and/or lanthanum, zinc, zirconium, manganese, oxidation inhibitor and magnesium. Alloy may additionally contain titanium, hafnium, aluminum, copper, nickel, silicon, silver, yttrium, thorium, iron and strontium. Alloys and articles manufactured from them possess high mechanical properties and high creep resistance at high temperature.

EFFECT: enhanced creep resistance of alloys.

21 cl, 7 dwg, 5 tbl, 2 ex

 

THE TECHNICAL FIELD TO WHICH THE PRESENT INVENTION RELATES.

The present invention relates to magnesium (Mg) alloys, and more particularly to magnesium alloys, which are creep resisting high temperatures.

PREREQUISITES FOR THE CREATION OF THE PRESENT INVENTION.

Magnesium alloys for many years of use in those applications where it is required that the material of construction has a high specific strength. Typically, you can expect to components derived from magnesium alloy, had a lot of constituting approximately 70% by weight of the component of aluminum (Al) alloy such volume. Aerospace, respectively, was significant consumer of magnesium alloys and magnesium alloys are used for many components in modern military aircraft and space vehicles. However, compared with aluminum alloys wider use of magnesium alloys prevent that they usually have lower creep resistance at elevated temperatures.

With growing demand control fuel consumption and reduce harmful emissions into the atmosphere worldwide car manufacturers are forced to develop vehicles that consume less fuel. To achieve this goal, the main factor is is the reduction of total mass of vehicles. The main element contributing to the weight of any vehicle is the engine, and the most significant component of the engine is the cylinder, the weight of which amounts to 20-25% of the total weight of the engine. In the past, significant savings in weight was obtained by replacing traditional block of grey cast iron cylinder block made of aluminum alloy, and an additional reduction of about 40% could be obtained if it could be used magnesium alloy that could withstand temperatures and mechanical stresses generated during operation of the engine. However, before considering the production line of a viable block of a magnesium alloy for the engine it is necessary to develop this alloy, which combines the desired mechanical properties at elevated temperatures with a cost-effective process. In recent years, the search for magnesium alloy that provides adequate mechanical properties at elevated temperatures, was focused mainly on the process of high pressure casting (HPDC), we developed several alloys. Casting under high pressure is considered to be the best choice for achieving a high capacity to neutralize probable high SRT is on basic magnesium alloy. However, casting under high pressure is not necessarily the best process for the production of a cylinder block of the engine and actually most of the block even get through the exact gravity casting in sand moulds or in sand casting under low pressure.

There are two main classes of magnesium alloys produced by casting in sand moulds.

(A) Alloys based on the binary system magnesium-aluminum, often with small additions of zinc (Zn) to increase strength and casting properties (fluidity). These alloys have adequate mechanical properties at room temperature, but do not work well at elevated temperatures and have poor mechanical properties at temperatures in excess of 150°C. These alloys do not contain expensive alloying elements and are widely used in areas, which do not require high strength at high temperatures.

(B) Alloys capable of grinding grain with the introduction of zirconium (Zr) Main alloying elements in this group are zinc, yttrium (Y), silver (Ag), thorium (Th) and rare earth (RE) elements, such as neodymium (Nd). In this description, the expression "rare earth" should refer to any element or combination of elements with atomic numbers from 57 to 71, from lanthanum (La) to lutetium Lu). With proper selection of the alloying elements of the alloy in this group can have excellent mechanical properties at room and elevated temperatures. However, with the exception of zinc alloying elements in this group, which includes additive, grinding grain, are expensive, which in result leads to the fact that these alloys are generally limited to aerospace applications.

Magnesium alloy ML10, developed in the Soviet Union, used for many years for castings intended for use in aircraft at temperatures up to 250°C. the Alloy ML10 is a high-strength magnesium alloy, developed on the basis of Mg-Nd-Zn-Zr. Alloy ML19 further comprises yttrium.

In article Mukhina and others, entitled "Investigation of microstructure and properties of flowable neodymium - and tricoderma magnesium alloys at elevated temperatures", published in "Science and Heat Treatment Vol.39, 1997, illustrates the typical composition (wt.%) alloys ML10 and ML19 have the following composition

ML10ML19
Nd2,2-2,81,6-2,3
Y01,4-2,2
Zr0,4-1,0 0,4-1,0
Zn0,1-0,70,1-0,6
MgRestRest
with levels of impurities, components
Fe<0,01
Si<0,03
Cu<0,03
Ni<0,005
Al<0,02
Be<0,01

Alternative alloys that have been developed are the alloys known in the prior art as alloy QE22 (alloy system Mg-Ag-Nd-Zr) and alloy EN (alloy system Mg-Nd-Zr-Th). However, these alternative alloys are expensive to produce because they contain significant amounts of silver and thorium, respectively.

Heat resistant magnesium alloys with crushed grain can be subjected to hardening by heat treatment T6, which involves heat treatment in solid solution at elevated temperature, followed by quenching (sudden cooling) and followed by artificial aging at elevated temperatures. During heating before quenching the excess phase go into solid solution. the process of aging refractory phases are in the form of fine submicroscopic particles and create microheterogeneity within grains of solid solution, blocking processes of diffusion and shear at elevated temperatures. This improves the mechanical properties, in particular the final strength in the long term and creep resistance of the alloys at high temperatures.

Up to the present time were not available measurable in sand casting magnesium alloys having the required properties at elevated temperatures (for example, at temperatures of 150-200° (C) at a reasonable price. At least preferred embodiments of the present invention relate to such alloy and the present invention, in particular, but not exclusively, focused on the application of technological operations in precision casting.

THE ESSENCE OF THE PRESENT INVENTION.

In the first aspect of the present invention provides a receiving base alloy of magnesium containing:

1.4 to 1.9 wt.% neodymium

0.8 to 1.2 wt.% rare earth element (REE), in addition to neodymium,

0.4 to 0.7 wt.% zinc,

0.3 to 1.0 wt.% zirconium,

0-0,3 wt.% manganese, and

0-0,1 wt.% inhibitor of oxidation (oxidation inhibitors),

the rest is magnesium except for incidental minor impurities.

In a second aspect the present invention provides for obtaining magnesium alloy containing:

1.4 to 1.9 wt.% neodymium

0.8 to 1.2 wt.% rare earth element (REE e is the elements), in addition to neodymium,

0.4 to 0.7 wt.% zinc,

0.3 to 1.0 wt.% zirconium,

0-0,3 wt.% manganese, and

0-0,1 wt.% the oxidation inhibitor,

not more than 0.15 wt.% titanium

not more than 0.15 wt.% hafnium,

not more than 0.1 wt.% aluminum

not more than 0.1 wt.% copper,

not more than 0.1 wt.% Nickel

not more than 0.1 wt.% silicon

not more than 0.1 wt.% silver,

not more than 0.1 wt.% yttrium,

not more than 0.1 wt.% thorium,

not more than 0.01 wt.% iron,

not more than 0.005 wt.% strontium,

the rest is magnesium except for incidental minor impurities.

Alloys according to the second aspect of the present invention preferably contain:

(a) less than 0.1 wt.% titanium, more preferably less than 0.05 wt.% titanium, preferably less than 0.01 wt.% titanium, and preferably essentially do not contain titanium,

(b) less than 0.1 wt.% hafnium, more preferably less than 0.05 wt.% hafnium, preferably less than 0.01 wt.% hafnium, and preferably essentially do not contain hafnium,

(c) less than 0.05 wt.% aluminum, more preferably less than 0.02 wt.% aluminum, preferably less than 0.01 wt.% aluminum, and preferably essentially do not contain aluminum,

(d) less than 0.05 wt.% copper, more preferably less than 0.02 wt.% copper, preferably less than 0.01 wt.% copper, and preferably essentially do not contain copper,

(e) less than 0.05 wt.% Nickel is, more preferably less than 0.02 wt.% Nickel, preferably less than 0.01 wt.% Nickel, and preferably essentially do not contain Nickel,

(f) less than 0.05 wt.% silicon, more preferably less than 0.02 wt.% silicon, preferably less than 0.01 wt.% silicon, and preferably essentially do not contain silicon,

(g) less than 0.05 wt.% silver, more preferably less than 0.02 wt.% silver, preferably less than 0.01 wt.% silver, and preferably essentially do not contain silver,

(h) less than 0.05 wt.% yttrium, more preferably less than 0.02 wt.% yttrium, preferably less than 0.01 wt.% yttrium, and preferably essentially do not contain yttrium,

(i) less than 0.05 wt.% thorium, more preferably less than 0.02 wt.% thorium, preferably less than 0.01 wt.% thorium, and preferably essentially do not contain thorium,

(j) less than 0.005 wt.% iron, and preferably essentially do not contain iron, and

(k) less than 0.001 wt.% strontium, and preferably essentially do not contain strontium.

Alloys according to the present invention preferably contain at least 95 wt.% magnesium, preferably with 95.5-97,0 wt.% magnesium, and preferably approximately the 96.3 wt.% magnesium.

The content of neodymium is preferably more than 1.5 wt.%, preferably more than 1.6 mA is.%, more preferably 1.6 to 1.8 wt.%, and preferably about 1.7 wt.%. The content of neodymium can be obtained by introduction of pure neodymium, and can also be obtained from a neodymium contained in the mixture of rare earth elements, such as mischmetall, or combinations thereof.

The content of rare earth element (REE), in addition to neodymium, preferably 0.9-1.1 wt.%, more preferably about 1 wt.%. Rare earth element (rare earth elements), in addition to neodymium, are cerium (CE), lanthanum (La) or their mixture. Cerium is preferably more than half the mass of the rare earth elements, in addition to neodymium, more preferably 60-80 wt.%, in particular about 70 wt.% with lanthanum, essentially constituting the rest. Rare earth element (rare earth elements), in addition to neodymium, can be introduced in the form of pure rare earth elements, and also introduced in the form of a mixture of rare earth elements, such as mischmetall, or combinations thereof. Rare earth elements, in addition to neodymium can be entered from cerium mischmetall containing cerium, lanthanum, optional neodymium, a small amount of parsetime (Pr) and trace amounts of other rare earth elements.

Orienting the plane of the eye-catching phases in alloys of the Mg-NdZn, relating to the content of zinc is prismatic at very low levels of Zn and base on the levels of more than about 1 wt.%. The best mechanical properties were obtained when the levels of zinc, which contribute to combining orienting planes. The zinc content is preferably less of 0.65 wt.%, more preferably 0.4 to 0.6 wt.%, more preferably 0,45-0,55 wt.%, and preferably about 0.5 wt.%.

The decrease in the iron content can be achieved by adding zirconium, which allocates iron from the molten alloy. In accordance with this, the content of zirconium specified in this application, is a residual contents of zirconium. However, it should be noted that zirconium can be implemented in two different stages. First, upon receipt of the alloy and, secondly, after the melting of the alloy immediately before casting.

The properties of the alloys of the present invention, at elevated temperature are dependent on adequate grinding of grains and for this reason it is necessary to maintain the level of the content of zirconium in the melt because of the value that you want to remove iron. For the required strengths in tension and compression, the grain size is preferably less than 200 μm, and more preferably less than 150 MCR. The relationship between creep resistance and grain size in the alloy of the present invention, is illogical. Conventional creep theory would predict that the creep resistance will decrease with decreasing grain size. However, the alloys according to the present invention, showed the least resistance to creep when the grain size of 200 μm and improvements in creep resistance at smaller grain sizes. For optimum creep resistance, the grain size is preferably less than 100 μm, and more preferably approximately 50 μm. The zirconium content should preferably be the minimum required to achieve a satisfactory removal of iron and adequate grinding of grain for the appropriate purpose. Generally, the zirconium content is more than 0.4 wt.%, preferably of 0.4 - 0.6 wt.%, and more preferably about 0.5 wt.%.

Manganese is an optional component of the alloy, which may be entered into if there is a need for additional removal of iron is higher than the value achieved by using zirconium, especially if the content of zirconium is relatively low, for example below 0.5 wt.%.

Elements that suppress or at least inhibit the oxidation of the molten alloy, such as beryllium (Be) calcium (CA) are optional components, which can be introduced especially in those cases when it is impossible to provide adequate protection of the melt by controlling the atmosphere of protective gas. That is, in particular, if the process of casting does not provide a closed system.

In the ideal case, the content of random impurities is equal to zero, but it should be obvious that this is essentially impossible. In accordance with this, it is preferable that the content of random impurities was less than 0.15 wt.%, more preferably less than 0.1 wt.%, even more preferably less than 0.01 wt.%, and more preferably less than 0.001 wt.%.

In a third aspect the present invention provides a receiving base alloy of magnesium, having a microstructure containing equiaxial grains of solid solution on the basis of magnesium, separated by grain boundaries by means of, in General, touching intergranular phases, the grains have a uniform distribution bicrystalline records of nanoscale on more than one plane - polarized plane containing magnesium and neodymium, intergranular phase contains almost entirely of rare earth elements, magnesium and the greatest amount of zinc, and rare earth elements are essentially the cerium and/or lanthanum.

Grain may contain small spherical and globular precipitates. Spheres of the economic groups can contain thin sterjnevye selection. Globular allocation can be mainly zirconium plus zinc atomic ratio of Zr:Zn, equal to approximately 2:1. Sterjnevye allocation can be mainly zirconium plus zinc atomic ratio of Zr:Zn, equal to approximately 2:1.

The expression "contiguous"as used in this description, means that at least a large part of intergranular phase is touching, but between other adjoining parts may be some gaps.

In the fourth aspect of the present invention provides a method of obtaining products from magnesium alloy, providing exposure to products obtained by casting alloy, corresponding to the first, second or third aspect of the present invention, heat treatment T6.

In the fifth aspect of the present invention provides a method of obtaining products from magnesium alloy, providing

(a) solidification of the casting alloy, corresponding to the first, second or third aspects of the present invention, in a mold,

(b) heating the solidified casting at a temperature of 500-550°during the first period of time,

(c) quenching the casting, and

(d) aging the casting at a temperature of 200-230°during the second period of time.

The first period of time is preferably 6-4 hours and the second period of 3-24 hours.

In the sixth aspect of the present invention provides a method of producing castings obtained from magnesium alloy, providing.

(1) melting alloy, corresponding to the first, second or third aspects of the present invention, for formation of the molten alloy

(2) the introduction of the molten alloy in a sand mold or permanent form and ensure solidification of the molten alloy

(3) removing the resulting casting mold, and

(4) the shutter speed casting in the first temperature range for a first period of time during which part intergranular phase casting dissolved, and the subsequent exposure of the casting in the second temperature range during the second time period, during which prompted the selection of records of nanoscale beans casting and at grain boundaries.

The first temperature range is preferably 500-550°With the second temperature range is preferably 200-230°With the first time period is preferably 6-24 hours, and the second time period is preferably 3-24 hours.

In the seventh aspect of the present invention provides a receiving cylinder of the internal combustion engine by using a method suitable the th fourth, the fifth and sixth aspects of the present invention.

In the eighth aspect of the present invention provides a receiving cylinder of the internal combustion engine of magnesium alloy, corresponding to the first, second and third aspects of the present invention.

Above are special references to blocks cylinder engines, but it should be noted that the alloys according to the present invention can be used in other applications at elevated temperatures and in low-temperature applications.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE PRESENT INVENTION.

Example 1

The samples were obtained by gravity casting of the six compositions of the alloy (see Table 1) in step flat mold having a stepped thickness from 5 to 25 mm for the formation of castings, as illustrated in figure 1 Rare earth elements, in addition to neodymium, was introduced in the form of mischmetall based on cerium (CE), which contains cerium, lanthanum, and a certain amount of neodymium. Additional neodymium and zinc were introduced in the form of their elements. Zirconia was introduced through a proprietary ligatures Mg-Zr. When receiving a flat castings used standard handling procedures melting. After that, some samples were subjected to heat treatment T6, specified in Tab is itzá 2 number 3, which was determined to ensure the best results. To prevent oxidation of the surface layers during the heat treatment heat treatment on the solid solution was carried out in an environment with a controlled atmosphere. The resulting heat treatment the samples were then subjected to examination and testing to determine the hardness, tensile strength, creep resistance, corrosion resistance, fatigue characteristics and changes while holding the load of the bolt. The details are given below in Table 1 and Table 2

Table 1
Estimated composition
no songsZn (wt. %)Nd (wt. %)Rarely. ZEM. the item, in addition to Nd (wt. %)Zr (wt. %)All redatam. elements (wt. %)
Comparative composition And0,421,401,330,472,73
Comparative composition0,852,041,130,5033,17
Comparative composition0,881,680,820,519 2,50
Inventive composition 10,411,630,80,4952,43
The inventive composition 20,671,640,810,4592,45
The inventive composition 30,551,700,940,552,64

Table 2
Estimated heat treatment T6
No. cat. processingProcessing on the TV. solutionThe type of rapid coolingAging
0525°C, 8 hWater 80°215°C,16 h
1525°C, 8 hWater 80°215°C, 4 h
2525°C, 4 hWater 80°215°C, 150 min
3525°C, 8 hWater 80° + quenching in water215°C, 4 h
4525°C, 8 hThe air215°C, 4 h
5525°C, 8 hWater 80° +quenching in water215°8 h
6525°C, 8 hWater 80° +quenching in water215°C, 150 min
7525°C, 4 hWater 80° +quenching in water215°C,4 h

From the analysis results, the following conclusions were made.

The micrograph showed that the comparative composition has the greatest number of intermetallic phases at grain boundaries and triple points, which is compatible with having the highest content of rare earth elements. Comparative composition C and composition, corresponding to this invention, have the least amount of intermetallic phase, which is also compatible with the presence of low total content of rare earth elements. Micrograph patentable composition 2 clearly showed a much larger and more variable grain size than any of the other songs. This may be due to the smaller content of zirconium (Zr) in this composition. All six compositions had accumulations of secretions, located approximately in the center of the borders, which are described elsewhere in this description as being a connection Zr-Zn.

Measurements of hardness and composition of the present invention 1 and 2 were good or better compositions of the invention 3, indicating that ovni content of zinc (Zn) of 0.4-0.6. % were acceptable. Comparative composition gave correspondingly low values of hardness, indicating that the combination of a high zinc content and a low content of rare earth elements is less acceptable. Comparative compositions a and b are very similar to the composition of the present invention, which may show that the negative impact of high zinc content can be compensated by very high contents of rare earth elements. However, it is not commercially attractive because of the high cost of rare earth metals.

Extension capacity was determined at room temperature and at temperatures of 100, 150 and 177°C. Options compositions were chosen so as to investigate the effect of multiple interactions, were made the following observations.

The composition of the invention 1, which is similar to the inventive composition 3 according to the content of neodymium, but has a lower content of zinc and other rare earth elements, has mechanical properties that are as good or better than using the composition of 3, indicating that low levels of zinc and/or rare earth elements is not necessarily a negative effect on mechanical properties.

Comparative composition a and composition 1 have very similar low the content of zinc, while comparative composition And has a lower content of neodymium, a higher content of other rare-earth elements and a higher total content of rare earth elements. At room temperature the composition 1 had a lower conditional yield strength and higher elongation, which is compatible with optional content of neodymium to ensure hardening and less intermetallic phase grain boundaries Ce/La. At elevated temperatures, the trend present at room temperature.

Compositions of the invention 1 and 2 and the comparative composition composition were very similar with the exception of zinc, which was more than in the comparative composition C. the Comparative composition has a slightly higher content of neodymium and other rare earth elements than composition 1 or 2. Both at room and at elevated temperatures it was found that with increasing zinc content of the conditional yield strength decreases and elongation increases. The most significant drop in the conditional yield strength is between 0.4 wt. % and 0.67 wt. % zinc.

Both comparative compositions b and C were very similar (high) content of zinc with a comparative composition having a higher total content of redkozemel is lnyh elements (higher content of neodymium and a higher ratio of Ce/La), than comparative composition C. Comparative composition was, respectively, better than the comparative compositions With respect to the conditional yield strength and relative elongation at all temperatures, there are two properties that have a significant impact on the nature of the changes creep.

The creep tests were performed on all compositions at constant load of 90 MPa and at temperatures of 150 and 177°C. Table 3 shows the speed creep steady state.

Table 3
Speed creep steady state (sec-1)
Load 90 MPa at a temperature of 150°Load 90 MPa at a temperature of 177°
Comparative composition And7,05×10-113,6×10-10
Comparative composition2,66×10-111,67×10-10
Comparative composition4,07×10-112,5×10-10
Inventive composition 15.56mm×10-115,31×10-10
The inventive composition 22,59×10-11 3,6×10-10
The inventive composition 32,80×10-111,40×10-10

When comparing different creep resisting magnesium alloys often refer to the load to obtain the values of the creep of 0.1% after 100 hours. None of these six compositions had no creep deformation of such order after 100 hours at a temperature of 150°and load 90 MPa. Similarly at a temperature of 177°With any one song does not exceed this value after 100 hours, although creep exceed values that have been achieved at a much longer test periods. At a temperature of 150°With all six songs would be acceptable in respect of their nature changes creep.

Effect of zinc observed in the results of tensile tests, it was also evident in the results of creep at a temperature of 150°With, in particular, in relation to the relative elongation at the initial stage of creep, where patentable composition 1 was better than patentable composition 2, which was, in turn, better comparative composition C. the Speed of the second stage of creep were the same in these three songs. Comparative composition, which had the highest content of zinc,but also had a high content of rare earth elements, was also acceptable, showing in this case that the negative impact of high zinc content can be neutralized through high contents of rare earth elements.

Comparative composition And had a higher initial reaction than patentable composition 1 and a slightly higher speed creep steady state, which indicates that although the content of neodymium 1.4 wt.% is acceptable, the content of 1.5 wt.% it would be preferable minimum, and the content of 1.6 wt.% even more preferred.

Example 2

The sequence of operations when the experiment

The alloy samples, indicated by the symbols SC1 (96,3 wt.% Mg, 1.7 wt.% Nd, 1.0 wt.% Re (Ce:La=70:30), 0.5 wt.% Zn and 0.5 wt.% Zr), was prepared from step plates, illustrated in figure 1, obtained by gravity casting. Cerium and lanthanum were introduced in the form of mischmetall based on cerium, which also contained some amount of neodymium. Additional neodymium and zinc were introduced in their basic forms. Zirconia was introduced through a proprietary ligatures Mg-Zr. The mechanical properties given in this application were determined from samples cut from 15 mm steps, where the resulting grain size was approximately 40 μm. In the preparation of cast plates used standard procedures for obtaining the melt and conditions t is micheskoj processing in a controlled environment.

The MICROSTRUCTURE of Samples for metallographic examination were polished using diamond paste with a particle size of up to 1 μm, followed by treatment of colloidal silica with a particle size of 0.05 microns. Etching was carried out in nitric acid with ethylene glycol and water for about 12 seconds.

TENSILE TEST AND COMPRESSION - extension Capacity was measured in accordance with the methodology E8 American society for testing materials at temperatures of 20, 100, 150 and 177°With air using a bursting machine brand "Instron". Before testing the samples kept at the temperature for 10 minutes. The test pieces had a rectangular cross-section (6 mm×3 mm) with a measuring base 25 mm (Fig 2(a)) ((approx. trans.) in the above drawing, the measuring base is indicated as having a length of 27 mm). The yield strength in compression was determined in accordance with the methodology e American society for testing materials at the same temperature, using cylindrical samples with a diameter of 15 mm and a length of 30 mm, a Modulus of elasticity of the alloy was determined at room temperature and at elevated temperatures using a piezoelectric ultrasonic composite oscillator [Robinson, WH and Edgar A IEEE Transaction on Sonics and Ultrasonics, SU-21(2) 1974 98-105].

CREEP TESTING - Character change the creep was determined on the machine constant load at temperatures of 150 and 177° With and voltages 46, 60, 75 and 90 MPa in a silicone oil bath with controlled temperature. Samples for testing had the same geometry as the samples for testing for tensile strength, and elongation during creep was measured directly from the measurement database samples.

TESTS FOR FATIGUE - Fatigue strength at 106and 107the cycles were determined at temperatures of 25 and 120°s on the air. Samples having a circular cross section with a diameter of 5 mm with a measuring base 10 mm (figure 2(b)), were polished to a surface roughness of 1 μm, which corresponds to the approximate surface finish in the main bearing is the most strenuous part of the engine block. The specimens were loaded axially and completely reversible tension-compression (i.e. at an average voltage of zero), and the measurement frequency was 60 Hz, corresponding to a nominal operating conditions. There are several procedures for assessing fatigue strength for this life, and in this work, we used the stepwise method (BS 3518 part 5).

TEST HOLDING the LOAD BOLT - Test holding the load of the bolt could be used to simulate the relaxation that may occur in the work under compression load. Test method [Pettersen and To Fairchild's SAE Technical Paper 970326] provides for the application of p is donacarney load (in this case, a value of 8 kN) through the site, consisting of two identical bushings thickness of 15 mm and an external diameter of 16 mm, obtained from the material to be tested, and high-strength bolt M8 equipped with a load cell (figure 3). Continuously measured the change in load for 100 hours at elevated temperature (150 and 177°). Two significant loads (when determining the nature of changes in the holding load of the bolt) are the initial load of PIwhen the ambient temperature and the load RFat the completion of testing after return to ambient conditions. The ratio of these two values (PF/PI) is a measure of changes in the retention alloy load bolt. Often there is an initial increase in load during heating of the United bolt node to the test temperature. This is the result of the combined thermal expansion of the United bolt node and the resulting deformation in the sleeve of alloy.

Thermal CONDUCTIVITY thermal Conductivity was measured on samples with a diameter of 30 mm and a length of 30 mm

CORROSION RESISTANCE - Corrosion resistance of the alloy SC1 was compared with the corrosion resistance of AZ91 alloy, using standard tests of immersion in saline solution at room temperature. The tests were carried out for seven days in medium salt solution (3.5% NaCl) with pH, the stable is to 11.0 units using 1 M NaOH solution. The corrosion products were removed from the samples for testing by washing in chromic acid, followed by rinsing in ethanol.

Results and their discussion.

MICROSTRUCTURE - As alloy obtained by casting in sand form, the alloy SC1 requires treatment T6 (heat treatment in a controlled atmosphere to obtain solid solution hardening in cold or warm water and annealing at elevated temperatures) for a complete formation of their mechanical properties. The recommended heat treatment is a balance between the requirements of mechanical properties and economically reasonable time after casting. Microstructure T6 alloy SC1, which is illustrated in figure 4, consists of grains of phase (A) α-Mg, blocked intermetallic phase (In), magnesium-rare earth elements on the grain boundary and triple points. In the Central regions of most grains are accumulations sterzhnevykh discharge (S). Intermetallic phase In the stoichiometric composition is close to the connection of Mg12(La0,43Ce0,57).

TENSILE STRENGTH AND COMPRESSION - figure 5(a) illustrates the tensile properties (0.2% of the conventional yield strength and ultimate tensile strength) the yield strength in compression depending on the temperature. Figure 5(b) illustrates the elongation at RA is over, as well as the temperature dependence. It should be noted that the mechanical properties of the alloy SC1 is very stable at elevated temperatures, and the conditional yield stress as tensile and compression remains relatively constant between room temperature and the temperature of 177°C. the properties of the alloy SC1 at room temperature anywhere nearly as high as most other magnesium alloys, obtained by casting in sand molds, but the stability of these properties up to a temperature of 177°makes this alloy is particularly attractive for applications in the engine block.

Table 4 shows the results of determination of modulus of elasticity and it should be noted that the modulus of elasticity has a fall of less than 10% at a temperature of 177°compared with the value of the modulus of elasticity at room temperature.

Table 4
The modulus of elasticity of the alloy SC1 defined using technology piezoelectric ultrasonic composite oscillator
Temperature (°)25100177
The young's modulus (GPA)45,8±0,343,9±0,341,9±0,3

THE CHANGING NATURE OF CREEP AND DERIVAN THE LOAD BOLT The microstructure of the alloy SC1 is very stable at temperatures up to 177°and this is an important factor together with the shape and distribution of the intermetallic phase in the grain boundaries in achieving the desired resistance to creep. The use of voltage creep, which is the voltage to obtain the deformation during creep component of 0.1% after 100 hours at temperature, as a measure of creep resistance, is an arbitrary measure, but, in spite of this, it is appropriate to compare the effect of creep of the alloy. Using this concept, the nature of changes in alloy SC1 can be compared with changes in the alloy A319 (6) and it is clear that these two alloy are very similar in their reactions creep in the temperature range 150-177°C. However, more importantly, it should be noted that the voltage required to obtain a strain of 0.1% during creep of alloy SC1 after 100 hours at a temperature of 150°and at a temperature of 177°approaching the limits of yield strength (offset of 0.2%) tensile material.

Typical curves retention load bolts for alloys SC1, A319 and AE at a temperature of 150°and With a load of 8 kN is shown in Fig.7(a). Alloy SC1 is able T6, alloy A319 is in a state after casting in sand form, and alloy AE is in a state after casting under the high pressure (i.e. all three of the alloy are in their normal operating condition). The increase in load that occurs at the beginning of the test, is the final result of thermal expansion of the United bolt node received less deformation in the alloy bushings. Two significant loadings are initial load PI(in this case, the load 8 kN) when the ambient temperature and the load at the completion of testing after return to ambient conditions PF. The ratio of these two values is taken as a measure of changes in the holding load of the bolt alloy was used in this case for comparison alloy SC1 with alloy AE casting under high pressure at temperatures of 150 and 177° (Fig.7(b)). The nature of changes in the holding load of the bolt at elevated temperatures and in this case reflects the stability of this alloy at high temperature and it is obvious that the alloy SC1 as good as the aluminum alloy A319, and in this respect superior alloy AE.

FATIGUE PROPERTIES - cylinder engine is continuously subjected to the effects of cyclic stresses during operation and for this reason it is necessary to ensure that the material selected for the block could withstand fatigue loading. Fatigue strength of alloy SC1 at cycles 106and 107defined as at a temperature of 24°and at a temperature of 120°and the value is s, in Table 5, represent the values of strength, giving a 50% probability of crack formation (probability of failure). The limits represent the voltage for 10% and 90% probability of failure. It should be noted that these results were obtained for a maximum of 107cycles, not 5×107cycles defined in the settlement criteria. Despite this, the strength is high enough to be considered alloy satisfying the goal.

Table 5
Fatigue strength (MPa) alloy SC1 at two temperatures (R=-1)
Temperature (°)106cycles107cycles
24≈8075±18
12074±971±7

the symbol ≈ indicates that it was tested only 12 samples, and not 15 as required in accordance with the standard.

CORROSION - Character changes as a result of corrosion of the alloy, both internal and external, is of paramount importance. Corrosion on the internal surfaces can be controlled by the use of lubricating and cooling means in combination with a careful design to ensure compatibility of all the metal is ical components in contact with the coolant fluid. The resistance to corrosion of external surfaces will largely depend on the composition of the alloy. There is no one test that could determine the corrosion resistance of the alloy in all environments, and thus, the alloy SC1 compared with alloy AZ91 when using a standard test of immersion in saline solution. Both alloy were in a state after the heat treatment T6 and it was found that the average weight loss during this time was for alloy SC1 0,864 mg/cm2/day, and for alloy AZ91 - 0,443 mg/cm2/day.

Thermal CONDUCTIVITY thermal Conductivity of alloy SC1 was found equal to 102 W/MK, which is slightly less than the value of thermal conductivity, originally defined in the settlement criteria. However, obtaining this information is not a difficult modification to the cylinder block to account for this, thermal conductivity values.

CONCLUSION

Alloy SC1 meets the following technical requirements:

0,2% of the conventional yield strength of 120 MPa at room temperature and 110 MPa at a temperature of 177°C.

Creep resistance is comparable to the creep resistance of the alloy A319 at temperatures of 150 and 177°C.

The fatigue limit at room temperature is more than 50 MPa.

This combination of excellent mechanical properties if the appreciation is the R temperatures and estimated profitability allows you to put, what alloy SC1 will become an economically viable alternative as the material for the cylinder block of the engine.

In the claims below, in the foregoing description of the present invention except in those places where the context otherwise requires language or necessary meaning of the word "include" or variations such as "contains" or "containing"is used in a sense which includes, that is, to determine the presence of these elements, but not precluding the presence or addition of additional elements in different variants of implementation of the present invention.

It should be obvious that although in this application, reference was made to the publication (publications), known from the prior art, this reference does not allow one to assume that any of these documents forms part of General knowledge in engineering in Australia or any other country.

1. The base alloy of magnesium, comprising, in wt.%: 1.4 to 1.9 neodymium, 0,8-1,2 cerium and/or lanthanum, and 0.4-0.7 zinc, 0.3 to 1.0 zirconium, 0-0,3 manganese, 0-0,1 oxidation inhibitor, the rest is magnesium, except for occasional minor impurities.

2. The alloy according to claim 1, in which the magnesium content of 95.5 and 97 wt.%.

3. The alloy according to claim 1, in which the content of neodymium is 1.6-1.8 wt.%.

4. The alloy according to claim 1, in which the content of cerium and/or lanthanum stood the focus of 0.9 to 1.1 wt.%.

5. The alloy according to claim 1, in which the mass of cerium is more than half the mass of cerium and lanthanum.

6. The alloy according to claim 1, in which the zirconium content more than 0.4 wt.%.

7. The alloy according to claim 1, in which the zinc content is 0.4 to 0.6 wt.%.

8. The base alloy of magnesium, comprising, in wt.%: 1.4 to 1.9 neodymium, 0,8-1,2 cerium and/or lanthanum, and 0.4-0.7 zinc, 0.3 to 1.0 zirconium, 0-0,3 manganese, 0-0,1 oxidation inhibitor, not more than 0.15 titanium, not more than 0.15 hafnium, not more than 0.1 aluminum, not more than 0.1 copper, not more than 0.1 Nickel, not more than 0.1 silicon, not more than 0.1 of silver, not more than 0.1 yttrium, not more than 0.1 thorium, not more than 0.01 iron, not more than 0.005 strontium, the rest is magnesium, except for occasional minor impurities.

9. The alloy of claim 8, in which the magnesium content of 95.5 and 97 wt.%.

10. The alloy of claim 8, in which the content of neodymium is 1.6-1.8 wt.%.

11. The alloy of claim 8, in which the content of cerium and/or lanthanum is 0.9-1.1 wt.%.

12. The alloy of claim 8, in which the mass of cerium is more than half the mass of cerium and lanthanum.

13. The alloy of claim 8, in which the zirconium content more than 0.4 wt.%.

14. The alloy of claim 8, in which the zinc content is 0.4 to 0.6 wt.%.

15. The base alloy of magnesium, in which the microstructure contains equiaxial grains of solid solution on the basis of magnesium released more than one orienting the plane of the plates of nanoscale consisting of magnesium is neodymium, at grain boundaries distributed intergranular phase consisting almost entirely of cerium and/or lanthanum, magnesium and small amounts of zinc.

16. The method of obtaining products from magnesium alloy, providing heat treatment T6 products obtained by casting alloy according to any one of claims 1 to 15.

17. The method of obtaining products from magnesium alloy, providing for (a) solidification of a casting alloy according to any one of paragraphs. 1-15 in a mold, (b) heating the solidified casting at a temperature of 500-550°during the first period of time, (c) quenching the casting, (d) aging the casting at a temperature of 200-230°during the second period of time.

18. The method of producing castings from magnesium alloy, providing

(i) melting the alloy according to any one of claims 1 to 15 for the formation of the molten alloy, (ii) the introduction of the molten alloy in a sand mold or permanent form and ensure solidification of the molten alloy, (iii) removing the resulting solidified casting from the mold, (iv) exposure of the casting in the first temperature range for a first period of time during which part intergranular phase casting dissolved, and the subsequent exposure of the casting in the second temperature range below the first temperature range, the second period of time, during which the inspired selection of plates of nanoscale beans casting and at grain boundaries.

19. The method according to p, in which the first temperature range is 500-550°With the second temperature range is 200-230°With the first time period of 6-24 h, and the second time period is 3-24 hours

20. The cylinder block of the internal combustion engine obtained by the method according to any of PP-19.

21. The cylinder block of the internal combustion engine obtained from a magnesium alloy according to any one of claims 1 to 15.



 

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