Effect of Pre-aging-Warm Forming Process Parameters on Microstructure and Properties of 7075 Aluminum Alloy
The 7075 aluminum alloy was pre-aged and warm formed at different pre-aging temperatures(85,100,120 ℃)for different pre-aging times(0-32 h)and forming temperatures(150,200,250,300 ℃).The effect of process parameters on the microstructure and properties of alloy was studied.The optimum process parameters were determined.The results show that with the extension of pre-aging time,the grain size of 7075 aluminum alloy had no obvious change,the amount of precipitated phase increased,and the hardness and strength increased first and then decreased.Compared with those at pre-aging temperature of 100,120 ℃,the number and the size of precipitated phases were smaller,the hardness and strength were larger,and the percentage elongation after fracture was smaller at the pre-aging temperature of 85 ℃.The hardness and strength decreased with the increase of warm forming temperature.The optimum pre-aging-warm forming process parameters were listed as follows:pre-aging temperature of 85 ℃,pre-aging time of 24 h,and warm forming temperature of 150 ℃.At this time,the alloy had the best comprehensive properties,which had the tensile strength and percentage elongation after fracture were 95％and 163％of those of the 7075-T6 aluminum alloy,respectively.Baking at 180 ℃ for 30 min after forming could improve the strength and reduce the ductility.
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