Metal surface deformation strengthening technology
Metal surface deformation strengthening technology is a process that applies mechanical force to the metal surface to cause it to undergo plastic deformation, thereby changing the surface structure and stress state to achieve the goal of improving surface hardness, wear resistance and fatigue strength. Its core principle is to use plastic deformation to refine the grain size and increase the dislocation density of the surface metal, forming a work-hardened layer. At the same time, residual compressive stress is introduced to offset the tensile stress generated by part of the working load and delay the generation and expansion of fatigue cracks. This technology does not require changing the chemical composition of the metal, but only achieves performance improvement through mechanical action. It is applicable to a variety of metal materials, such as steel, aluminum alloys, titanium alloys, etc., and is widely used in aerospace, automobile manufacturing, mechanical engineering and other fields, such as the strengthening treatment of engine blades, springs, gears and other parts.
There are various types of metal surface deformation strengthening technologies, the most common of which include shot peening, rolling strengthening, internal hole extrusion, and ultrasonic impact strengthening. Shot peening is one of the most widely used technologies. It uses high-speed projectiles (such as steel shots and glass shots) to impact the metal surface, causing plastic deformation of the surface layer. The size, speed, and injection angle of the projectile can be adjusted according to the requirements of the part to obtain a strengthening layer of varying depths. It is suitable for surface strengthening of parts with complex shapes. Rolling strengthening uses hard rollers or balls to apply pressure to the metal surface, causing plastic deformation of the surface layer. It is commonly used to strengthen the outer cylindrical surfaces and flat surfaces of shafts and rods. It can simultaneously reduce surface roughness and improve dimensional accuracy.
Internal hole extrusion technology is mainly used to strengthen the inner hole surface of metal parts. By applying pressure to the hole wall through extrusion tools (such as extrusion heads and extrusion taps), the inner surface undergoes plastic deformation, forming a strengthening layer, thereby improving the wear resistance and fatigue strength of the inner hole. It is widely used in the processing of parts such as engine cylinder liners and hydraulic cylinders. Ultrasonic impact strengthening uses ultrasonic excitation to stimulate the impact head to perform high-frequency impact on the metal surface, causing plastic deformation. It is particularly suitable for strengthening the weld area, and can eliminate welding residual tensile stress and improve the fatigue strength of the weld joint. In addition, there are new technologies such as laser shock strengthening, which uses the shock waves generated by high-energy lasers to cause plastic deformation of the surface. It has the advantages of significant strengthening effect and small heat-affected zone.
The process parameters of metal surface deformation strengthening technology have a significant impact on the strengthening effect, mainly including deformation amount, loading speed, tool material, etc. If the deformation is too small, the strengthening effect is not obvious; if the deformation is too large, it may cause surface cracking or performance deterioration. The appropriate deformation needs to be determined based on the material properties and part requirements. The loading speed affects the uniformity of plastic deformation. High-speed loading (such as shot peening and ultrasonic impact) can obtain a more uniform strengthening layer; low-speed loading (such as rolling) is easier to control the deformation. The tool material needs to have high hardness and wear resistance, such as high-speed steel, cemented carbide, etc., to ensure the stability of the strengthening process and the service life of the tool.
Metal surface deformation strengthening technology offers numerous advantages, including simple processing, low cost, environmental friendliness, and applicability to a wide variety of part shapes. Compared to heat treatment strengthening, it eliminates the need for high-temperature heating, thus avoiding oxidation, decarburization, and deformation of parts. Compared to coating technologies, the strengthening layer is metallurgically bonded to the substrate, eliminating the issue of insufficient bonding strength. However, this technology also has limitations, such as the shallow depth of the strengthening layer (typically 0.1-2mm), which may be insufficient for heavily loaded parts. It is also prone to surface cracking in high-hardness, low-ductility metal materials.
With advances in industrial technology, metal surface deformation strengthening technology continues to develop. The application of equipment such as automated shot peening and CNC rolling has improved the precision and efficiency of the strengthening process. The use of new shot materials (such as ceramic and resin shot) has improved the strengthening effect and reduced surface damage. The application of computer simulation technology has enabled mechanical analysis and parameter optimization during the strengthening process, improving the stability of the strengthening quality. In the future, this technology will be combined with other surface treatment techniques, such as coating after shot peening to form a composite strengthening layer, further enhancing the overall performance of metal parts and meeting even more stringent application requirements.
