The Effect Of Homogenization Heat Treatment Process On Microstructure And Property For 6061 Aluminium Alloy

Al-Mg-Si alloy is 6XXX series aluminum alloy that can be significantly hardened by a proper heat treatment. Due to its good machinability, higher corrosion resistanee and better weld ability, it has broad applieations in spacelight, automobile parts and other parts. However, non-equilibrium eutectic phases of as-cast alloy led to poor plasticity of aluminum alloy subsequent deflection which had become the bottlenecks of Al-Mg-Si alloy forming. In order to improved the hot formability of as-cast aluminum alloy, and eliminated the non-equilibrium eutectic phases, homogenization heat treatment was used usually. Aluminum alloy was sensitive to the homogenization heat treatment, and different processes could lead to significant difference of material property. In conclusion, homogenization heat treatment was necessary to complex Al-Mg-Si alloy, which could be researched carefully.Based on 6061 aluminum alloy as the research material, this paper studied the effects of different homogenization heat treatment conditions（including the different heating temperature, holding time and cooling method） on evolvement rule for microstructure and property, discussed the inernal relation between the microstructure and property. Through comprehensive comparison and analysis, the appropriate processing parameters of 6061 aluminum alloy homogenization heat treatment could be acquired.Based on microstructure experiments and mechanical properties experiments, with increasing the homogenization temperature or prolonging the holding time, the non-equilibrium eutectic phases of as-cast structure are dissolved into the matrix gradually, the white net structure become discontinuous, and Mg₂Si and Si were dissolved into matrix, and acicular β-Al Fe Si, β-Al5（Fe Mn）Si phases transformed to spherical α-Al₁₂（FeMn）₃Si, α-Al₈（FeMn）₂Si, α-Al₁₂（FeMn）₃Si₂ phases gradually. After the holding time of homogenization reached 8h, the area fraction of the second phases reduced from 2.48% to 0.97%, and kept unchanged. Homogenization heat treatment could improved the property of alloy. In the process of tensile experiments, with the rising of heating time and extention of holding time, the trend of ductility and reduction of area firstly increased and then decreased, and values respectively attained to the maximum at 575℃ and 10 h. The fracture mechanisms were ductile fracture. By increasing the speed of cooling, the（Fe+Mn）/Si atomic ration and morphology of iron-rich phase could be changed, ductility and reduction of area for alloy were also increasing, and fracture mechanisms of alloy were ductile fracture.Combined with the experimental results and the factory actual production conditions, the proper homogenizing process of 6061 alloy is at 570-580℃ for 8-10h, air cooling.