Study On Mechanical Properties Of AZ91D Magnesium Alloy By Laser Shock Peening And New LSP System Process

Magnesium alloy has a low density(about 1.8 g/cm~3),good damping performance,large modulus of elasticity,high specific strength,and can withstand large impact loads.Due to these superior properties of magnesium alloys,they are widely used in aerospace,transportation,chemical,automotive and other industrial fields.With the development of the automotive industry,the demand for lightweight and environmental protection is becoming more and more obvious.High-performance and light-weight parts have higher requirements on the mechanical properties of magnesium alloys.Surface modification of magnesium alloy can improve the mechanical properties and fatigue life of magnesium alloy.However,traditional surface modification techniques such as shot peening and rolling have limited depth of influence on the material,so the surface modification of the material is carried out by laser shock peening method,which solves the disadvantages of low absolute strength of magnesium alloy and fatigue at room temperature,effectively inhibits the initiation and propagation of cracks in materials,and improves the application range and service life of magnesium alloys.This paper took AZ91D magnesium alloy as the research object,and the laser shock peening of different process parameters,tensile test and friction test were carried out.The following are the main research contents and conclusions:Laser shock peening was applied to magnesium alloy specimens with different spot overlap rate.The tensile test was used to explore the effect of spot overlap rate on laser shock peening effect.The results show that with the increase of the spot overlap rate,the impact strengthening effect is obviously improved,but the specimen with the spot overlap rate of 75%is not greatly improved compared with the tensile test performance of the 50%sample,considered the impact enhancement effect and economic factors,the appropriate spot overlap rate is 50%.Different times of laser shock peening treatment on the surface of magnesium alloy,the effect of laser shock peening on microhardness,friction and tensile properties of magnesium alloy was studied.Studies have shown that laser shock peening can significantly improve the microhardness of magnesium alloy,effectively improve the tensile strength and yield strength,and the average friction coefficient will decrease with the increase of the times of laser shock peening.According to the analysis of the tensile test results,the laser shock peening will bring about the roughness increase and the negative effect of the pit on the surface of the test piece,and there is a positive and negative effect balance in the laser shock peening process.Analysis of the tensile specimens observed by scanning electron microscopy(SEM)revealed that there were a large number of tearing ribs and equiaxed axons in the tensile fracture of untreated magnesium alloy specimens.The magnesium alloy specimens subjected to laser shock peening showed the fracture characteristics of the quasi-cleavage plane.At the same time,the influence mechanism of laser shock peening on the size of friction wear scar and the effect of material hardness on plough-groove wear marks were also analyzed.With the increase times of laser shock peening,the friction coefficient and wear scar size of magnesium alloy specimens gradually decrease,the hardness of the material increases,and the furrow wear scar decreases.SEM was used to observe the microscopic morphology of the bottom of the wear scar.It was found that the untreated magnesium alloy specimens were mainly fatigue peeling wear,and the magnesium alloy specimens subjected to laser shock peening were mainly abrasive wear.The traditional laser shock peening system has some shortcomings,such as poor stability of water film formed by side water spraying,difficult uniform control of water film thickness,impact of sputtering after shock wave,low energy coupling rate and so on.In view of the problems existing in the traditional laser shock peening system,this paper innovatively adopts new technologies such as coaxial water supply and mobile absorption layer,and builds a new laser shock peening system.The shortcomings of traditional laser shock peening system,such as slow processing speed and poor stability of water film,are basically solved.In addition,the5052 aluminum alloy was treated with a new laser shock peening system.The friction test of the test piece before and after the treatment was carried out.The results show that the friction performance of the test piece after the new laser shock peening is improved,and the feasibility of the new laser shock peening system is verified.