Method of surface heat treatment of metals
The invention relates to the field of engineering and is used to reduce the surface roughness of the crystallizing melt, increasing the density of the emerging structures and formation of residual compression stress in the processing of highly concentrated sources of radiation energy by controlling the hydrodynamic condition of the melt, while ensuring a stable laminar (close to hospital) flow regime. When the melt on the surface influence of an alternating electromagnetic field, the intensity of which is higher than the value corresponding to the magnetic saturation of the processed material in the volume of the melt, with the plane of the lines of force of the magnetic induction set perpendicular to the direction of movement of the melt. The technical result - the reduction of high-rise roughness parameters of the workpiece and the increase in strength properties. 1 Il.
The invention relates to mechanical engineering and can be used to reduce the surface roughness of the crystallizing melt, increasing the density of the emerging structures and formation of residual compression stress when oblablablama while providing a stable laminar (close to hospital) flow regime.
There is a method of stirring molten conductive metal in the ladle under the action of a magnetic field .
The disadvantages of this method are the complexity of the traffic control fluid flow and the inability to localize traffic control in certain areas of the melt.
The known method of surface heat treatment of metals, which is improving the surface quality of the crystallizing melt by reducing the speed of hydrodynamic flows in them .
The disadvantage of this method is the necessity of introducing into the structure of materials with special additives that restricts fluid flow and altering the chemical composition of the material.
The objective of the invention is the provision of a hydrodynamic equilibrium melt without special additives.
The technical result - the reduction of high-rise roughness parameters of the workpiece and the increase in strength properties.
This is achieved by a method of surface heat treatment of metals by laser melting, in which the speed control of hydrodynamic mixing of the melt in the zone of melting, act when fusing on the processed surface of the PE the Oia of the processed material in the volume of the melt, thus a plane of force lines of magnetic induction set perpendicular to the direction of movement of the melt.
It is known that if the melt has electrical conductivity and there is an electrical circuit, the result of its motion in a magnetic field, an electric current (EDS). Conversely, the current can coil due to a change in magnetic field (alternating magnetic field). The cause of electricity in the first case is turbulent flows in the volume of the melt, due to the action of thermocapillary forces in thermal expansion with simultaneous transition of a material in a liquid state. However, given the relatively uniform distribution of energy density on the surface area and the aperture of the beam (for example, when processed by a laser beam), the motion vector melt flow is directed to the surface. As a result of crossing conductive melt lines of magnetic induction of external field occurs induced magnetic field in the melt, disturbing externally induced field. In addition, due to the interaction of currents and fields, you receive the electromagnetic force, providing the response to the initial movement.
Indeed, the liquid is not suitable for all kinds of the electrical currents. The conductivity of the liquid due to the contained free charges (ions or electrons), which can move in an arbitrary manner; also, the fluid may be dielectric and contain related charges (molecular dipoles). The reaction of the electromagnetic force causes pseudophakia and dissipative effects of driving restrictions (with the mutual perpendicularity direction and magnetic field lines emerging force exactly protivonapravlennyh movement), pseudoplusia and conservative effects of excitation or strengthen existing traffic, as well as its deformation (change path), or to modify the flow structure in the Central and border areas of the melt (at intermediate angles between the velocity and the field lines of force are also a component normal to the velocity of motion, which distorts the original trajectory, seeking to direct the motion along the field); if parallel motion paths and power lines of interaction there is no effect.
Thus, the induced currents will tend to prevent relative motion between the fluid and the field, so the field will be “transferred” fluid. Limitation of turbulence busload speed and the pressure in the melt, that results in a more uniform relief of the surface of the liquid bath and reduces high-rise roughness parameters.
The liquid melt is a solid environment and therefore is characterized by pressure and speed. When this conductive ability of melt most metals allow you to use a property of a fluid to deform indefinitely (to thicken) as a factor increasing the density of the formed structures. The seal is ensured due to the actions of three-dimensional (compressive) forces, which push the metal from the inductor, resulting in the melt when the current flow and its interaction with its own magnetic field. Due to the fact that in the zone of fusion cross section of the inductor selected more dense than within the uncultivated areas of the surface, provided the diameter change of the beam current thread and the increase of the transverse bulk of the forces that cause local compaction of the material. When cooled in a magnetic field and crystallization in the bulk of the melt formed a favorable residual compressive stress, which increases the uniformity of structure.
The drawing shows a diagram of the surface treatment of metal surfaces by melting in a magnetic field.
The way the wasp the displacement is 1. The sample is placed in the solenoid 2. The solenoid is positioned so that when processed by a beam of plane force lines of the magnetic induction 3 is parallel to the processing surface 1. Then induce an alternating electromagnetic field 4, the tension of which is set higher than the value corresponding to the magnetic saturation of the material in the volume of the melt 5, after which produce radiation exposure. In the process of heating the metal in the volume of the melt 5 changes its state of aggregation, moving in the liquid phase. The induced ring currents 6 in the selected projection image is projected into a point. Gradient 7 section solenoid 2 marked difference in the cross sections of the beam current threads, high density which falls on the area of laser irradiation. Thermal movement 8 of the melt 5 in an alternating field 4 causes e.r.s. 9 (projected point) in the melt. The interaction of the current 6 in the volume of the melt 5 with its own magnetic field 3 is manifested in the form of bulk forces 10, oriented normal force lines of the magnetic induction and the compressive metal, facilitating its seal. Crystallization was carried out in the electromagnetic field 4 at a constant orientation.
Example 1. Produce locals 150 NS at the spot diameter 1.5 mm The treatment is carried out in a magnetic field of the solenoid when tension 350 kA/m Microhardness in the zone melting was 12400 MPa at a surface roughness Ra 1.25 μm. For samples processed according to traditional technology, the value of microhardness was 10400 when roughness Ra 6.8 μm and a residual compression stress of 450 MPa.
Example 2. Produce local pulse laser beam on the surface of the aluminum alloy B95 at a power of 0.8 kW and pulse duration of 100 NS when the spot diameter 2.0 mm, the Treatment is carried out in a magnetic field of a coil when the field strength is 740 kA/m, the surface Roughness was Ra 0.68 μm when the original 1.3 μm.
Example 3. Produce local pulse laser beam on the sample surface from bronze BRB with the power of 1.2 kW and pulse duration of 130 NS at the spot diameter 1.5 mm, the Treatment is carried out in a pulsed magnetic field of a cylindrical solenoid with a field of 1200 kA/m and pulse duration 110-5C. the surface Roughness was Ra 1.35 μm when the original 2.4 ám.
Sources of information
1. Shercliff J. The rate of magnetic hydrodynamics. M.: Mir, 1967, - 320 C.
2. Laser termouprochnenija cutting tools: About restoy heat treatment of metals by laser melting, at which carry out the speed control of hydrodynamic mixing of the melt in the zone of melting, characterized in that act when the melt on the surface of an alternating electromagnetic field, the intensity of which is higher than the value corresponding to the magnetic saturation of the processed material in the volume of the melt, with the plane of the lines of force of the magnetic induction set perpendicular to the direction of movement of the melt.