Study Of Hot Tearing Sensitivity And Properties Improvement Of Recycled 6061 Aluminum Alloy

Aluminum alloys have been widely used for their remarkable characteristics of high specific strength,high corrosion resistance,easy processing,and so on.With the consumption of aluminum resources and increasing pressure of environmental protection,the recycling of aluminum alloy is imminent.The 6XXX wrought aluminum alloys represented by 6061 has a large amount of market share.However,the particularly complex compositions of recycled aluminum after remelting,and the large tendency of hot tearing hinder the wider application of recycled aluminum.In this paper,the problems existing in the recycling process of recycled6061 aluminum alloy were systematically investigated.The melt treatment and element composite alloying were carried out for the recycled 6061 alloy to improve the mechanical properties reduce the hot tearing sensitivity of castings.Subsequently,the composite treated was subjected to rolling deformation,and then its heat treatment parameters were optimized,It's mechanical and wear properties were further studied.The compositions of recycled 6061 aluminum alloy are complex,and especially,the contents of impurity elements like Fe and Cu are high.In addition to Mg,all other elements are tending to increasing the tendency of hot tearing in the cast ingot of recycled aluminum alloy.The research results of alloy elements'effects on hot tearing sensitivity of recycled aluminum alloy are in good agreement with the statistical results.The control of Mg content is the key to reducing hot tearing sensitivity.The increase of Mg content can shorten the solidification interval and increase the content of Mg₂Si eutectic phase at the end of solidification.Due to the combined effect of shrinkage in the brittle temperature range and eutectic reaction shrinkage at the end of solidification,the hot tearing sensitivity decreased first and then increased.When the Mg content was 1.2%,the hot tearing sensitivity was small.The increase of Si,Fe and Mn content in the alloy promoted the formation of a large number of Fe-rich phases such as Al₁₃Fe₄,Al Fe Si and Al₁₅?Fe Mn?₃Si₂.The liquid phase flow and shrinkage is hindered and the grain boundary binding force is weakened resulting in the increase of the hot tearing sensitivity of the recycled 6061 alloy.The increase of Cu and Zn content in the alloy led to the increase of the low melting point Al₅Cu₂Mg₈Si₆ phase and the solidification interval of the alloy.Consequently,the strength and plasticity of the alloy near the solid phase line are reducedand the hot tearing resistance of the alloy increased.The grains of the recycled alloy were refined by Al-5Ti-0.3B-0.2C/Al-10Sr composite melt treatment.The needle-like Fe-rich phase were transformed into Chinese characters,which has a better connection with the aluminium matrix and thus contribute to the hot tearing resistance of the alloy.After the composite melt treatment,the recycled 6061 aluminum alloy with Mg content of1.2%?noted by recycled 1.2Mg/6061 aluminum alloy?exhibited a lower hot tearing sensitivity and better tensile mechanical properties.The optimal heat treatment process of recycled1.2Mg/6061 aluminum alloy was solution treated at 540?for 4h and then aging treated at180?for 10h.The tensile strength and hardness of recycled 1.2Mg/6061 aluminum alloy after rolling and heat treatment were 334.2MPa and 119HB,which were 13%and 16.7%higher than 6061 recycled aluminum alloy.The wear mechanism of recycled 1.2Mg/6061 aluminum alloy is mainly the coexistence of adhesive wear and abrasive wear.Its friction coefficient and the wear weight loss are 18.6%and 22%lower than the recycled 6061 aluminum alloy.In this paper,a composite treatment process of recycled 6061 aluminum alloy melt was suscessfully developed.The process can significantly reduce the hot tearing sensitivity of recycled 6061 aluminum alloy melt and improve its mechanical and wear properties.The results of this study are of great value to improve the reutilization quality of the recycled aluminum alloy.