Research On Grain Size Control And Performance Optimization Of Extruded 6061 Aluminum Alloy For Schock Absorber

Due to the increasingly serious global problems such as the greenhouse effect and energy shortage,it is a general trend to use low-density high-strength materials instead of traditional steel to achieve automotive lightweight.6061 aluminum alloy is widely used as automotive parts because of its low density,medium strength,good plasticity and corrosion resistance.Hot extrusion is one of the main processings for the alloy profile production.The grain size of the extruded material has an important impact on its performance and service life.In this paper,extruded 6061 aluminum alloy for automobile shock absorber was taken as the experimental materials,and casting,extrusion and heat treatment of the alloy were studied to explore the method of grain size controling and performance optimization of extruded material.Firstly,the effects of Al-5Ti-1B,Al-5Ti-1B-10RE and Al-5Ti-0.2C on the microstructure and mechanical properties of 6061 aluminum alloy were studied,and compared with those of 6061 alloy ingot for shock absorber production（HM ingot）;Secondly,the above-mentioned ingots were used for hot extrusion experiments to analyze the influence of extrusion temperature on the microstructure and mechanical properties of extruded materials;Finally,the effect of heat treatment on the microstructure and properties of the alloy were studied,and the corrosion resistance of T6 rods were compared with that of T6 shock absorber.The results of the casting experiments show that,the grain size of the 6061 aluminum alloy ingots with the addition of RE refiner and C refiner is significantly refined as compared with HM ingot.Among them,the RE refiner has the best refining effect,and the average grain size of the ingot is the smallest,about 100.9μm;the mechanical properties are the best,the tensile strength and elongation are 164 MPa and 15.8%,respectively,which are 27.2%and 42.4%higher than those of HM ingot.The results of hot extrusion experiments show that,the average grain size of 6061aluminum alloy extruded rods increases continuously with the increase of extrusion temperature;at the same extrusion temperature,the average grain size of RE ingot extruded rods is the smallest,and the grain size of the ingot extruded at 400℃is the finest（32.1μm）.This is because the grain size of the ingot has an effect on the dynamic recovery and recrystallization during thermal deformation.And,it is easier for the cast ingot with small grains to obtain a uniform and fine microstructure through extrusion.The mechanical properties of the ingots after extrusion are significantly improved.The RE ingot extrusion rods at the same extrusion temperature have more excellent mechanical properties.The tensile strength of the alloy rods extruded at 500℃reaches the maximum（222 MPa）,with an elongation of 24.4%,and the mechanical properties are significantly improved compared to the shock absorber sample.The results of heat treatment experiment show that,the shock absorber sample reaches the peak hardness after of aging at 160℃×10 h with solid solution at 550℃×80 min,due to the strengthening effect of theβ"precipitated phase,the corresponding tensile strength is 328 MPa,and the elongation is 11.8%.According to grain size statistics of T6 rods with different refiners,the average grain size of T6 treated RE extruded rods at 400℃is the smallest（47μm）,and its tensile strength and elongation are 345 MPa and 23.2%respectively,which are 17.7%and 46.6%higher than the T6 shock absorber samples.Corrosion results show that the alloy corrosion products are mainly Al（OH）₃.The shock absorber has the worst resistance to intergranular corrosion,and the maximum depth of intergranular corrosion reaches 512μm;while the resistance of the RE extruded sample to intergranular corrosion is significantly improved,the maximum corrosion depth is reduced to 241μm.