Effect Of Combined-heat Treatment On Microstructure,Mechanical Properties And Wear Characteristics Of As-cast Al-Si Alloy

With the rapid development of China's economic environment,environmental issues have become increasingly serious.To achieve the goal of energy conservation and emission reduction lighter materials has become a focus of social attention.With the increase of aluminumization rate in the automotive industry,people's requirements for the strength,plasticity and wear resistance of cast aluminum alloys are constantly increasing.In this paper,the influences of combined-heat treatment on the microstructure and mechanical properties of A356 and Al-10Si-5Cu-0.75Mg-0.55 Mn alloy were researched by methods of OM,SEM,TEM,DSC and so on.the friction and wear properties after different treatment processes under different loads were also studied.Above that,the mechanism of combined-heat treatment and the role of cryogenic treatment was explored.The results are as follows:The optimal combined-heat treatment processes of A356 and Al-10Si-5Cu-0.75Mg-0.55 Mn alloy are cryogenic treatment at-196 ? for 3 h plus solution at 510 ? for 5 h and water quenching plus artificial aging at 170 ? for 6 h;Solution at 495 ? for 6 h and water quenching plus cryogenic at-196 ? for 12 h plus artificial aging at 185 ? for 6 h.Compared with T6 treatment,the strength,elongation and hardness of A356 alloy increased by 11.4%,12.8% and 40% respectively.The strength and hardness of Al-10Si-5Cu-0.75Mg-0.55 Mn alloy was increased by 30% and 38%,the elongation was basically retained.The combined-heat treatment narrowed the secondary dendrite spacing and refined and dispersed the eutectic silicon particles and improved the roundness of the silicon particles of A356 alloy;Refined and rounded undissolved second phase particles,and significantly increased the number of precipitated phases and enlarged the proportion of ?? phases in the Al-10Si-5Cu-0.75Mg-0.55 Mn alloy,which enhances precipitation strengthening effect.Compared with T6 treatment,the combined-heat treatment samples of A356 alloy and Al-10Si-5Cu-0.75Mg-0.55 Mn alloy had better friction and wear properties.Under low load,the wear rate of the combined-heat treatment state was close to the T6 alloy.With the increase of the load,the wear rate of the combined-heat treatment was obviously reduced.The data of real-time recording of friction coefficient showed that the friction coefficient of the combined-heat treatment state is less fluctuating and the time required to enter the stationary phase was the shortest.The analysis of the grinding surface of the alloy shows that: two kinds of alloy were abrasive wear under low load but combined-heat treatment reduced furrow depth.Under high load the A356 alloy was delamination wear and combined-heat treatment reduced area.After combined-heat treatment Al-10Si-5Cu-0.75Mg-0.55 Mn alloy still showed abrasive wear,which indicated that the wear condition is lighter.According to the microstructure,the different processes of combined-heat treatments can effectively improve the mechanical properties and wear resistance of the alloy.A356 alloy should use the cryogenic-solution-aging treatment.It can refine the alloy grains and accelerate the diffusion and spheroidization of the silicon phase,which plays a role of grain refinement.Al-10Si-5Cu-0.75Mg-0.55 Mn alloy should use solution-cryogenic-aging combined-heat treatment.It can refine and dispersion the undissolved second phase and promote the precipitation of solute atoms to form GP-zone,which inoculated nucleation for the precipitation.And the precipitation strengthening effect was greatly enhanced to significantly improve the mechanical properties.