Research On Thermal-mechanical Hybrid Treatment Process And Mechanical Properties Of Magnesium Alloy

Magnesium alloys have a great application potential in the aerospace,automobile,electronics fields due to their low density,high specific strength and light weight,etc.However,the disadvantages of low strength,poor wear resistance and so on limit its application in industries.In this paper,the two strengthening processes of AZ31magnesium alloy,solid solution aging treatment and laser shock peening composite strengthening and homogenization annealing and laser shock peening composite strengthening,are investigated by the numerical simulation and experimental investigation.The variation rule of microstructure and mechanical properties of AZ31magnesium alloy were explored to provide a theoretical basis for expanding the application of magnesium alloys.Based on the platform of ABAQUS finite element software,Mg alloy matrix and precipitate phase were effectively combined by the bundled constraint method,and then the three-dimensional finite element model of Mg₁₇Al₁₂/Mg was established.Its mechanical response to laser shock effect and the shock wave propagation law were analyzed.The results show that the precipitated phase particles hinder the propagation of stress waves.The fine particles can store more energy,generating higher residual compressive stress and forming a deeper stress layer.The larger precipitated phase particles can produce high stress concentration.The orientation of the precipitated phase particles has a significant effect on the mechanical response of the matrix.In the case of mixed orientation,the residual compressive stress is higher and the ability to resist deformation is stronger.The research shows that during the solid solution aging treatment and laser shock peening hybrid strengthening process,the laser impact induces severe plastic deformation on the surface of magnesium alloy.The formed dent morphology is basically in accordance with the simulation results.Laser shock peening can further increase the microhardness of magnesium alloy after solid solution aging treatment.The microhardness of magnesium alloy sample aged for 16h is increased by 27.5%after laser shock peening compared to original sample.And the tensile strength is also improved at a certain degree,but the elongation is decreased.The tensile fracture morphology indicates that the fracture behavior of surface strengthening layer of magnesium alloy changes after laser shock peening.The fracture morphology features of large cleavage planes and tear ridges are mainly presented.Homogenization annealing and laser shock composite strengthening enhance the mechanical properties of magnesium alloys.The microstructure of homogenized sample mainly consists of?-Mg matrix phase and second phase particle.The composition of second phase particle is mainly Al element,and contains Mg and Mn elements as well.The homogenization annealing and laser shock peening hybrid process improved the microhardness and tensile strength of original samples,increased respectively by 41.5%and 20.3%compared with the original sample.The fracture morphology of surface strengthening layer of the sample after laser shock peening is mainly shown as the cleavage planes,cleavage steps and tear ridges,exhibiting brittle fracture characteristics.This is consistent with the decreased elongation of the homogenized sample after laser shock peening.