Study On Heat Treatment Of 6016 Aluminum Alloy Sheets For Automotive Body

At present, extensive application of high-quality aluminum alloy sheets for automotive body is baffled by foreign monopoly of the key heat treatment technology and equipment. The experiment material of this research is 6016 aluminum alloy. The effects of solution time and cooling method on the dissolution of alloy phases, recrystallization, formability and the bake-hardening ability of cold rolled 6016 aluminum alloy, also the effects of pre-aging temperature within the range of 80～180℃, pre-aging time within the range of 1-15min on the formability and the bake-hardening ability during paint baking of 6016 alloy sheets, which were holding at room temperature(RT) before pre-aging for 5min and 60min respectively after solution at 550℃ for 5min then water quenched, were examined in this research. The purpose is to develop the appropriate heat treatment to improve formability and the bake-hardening ability of 6016 aluminum alloy, and to provide theoretical support for the industrial production. The results of this reasearch are as follows:(1) The recrystallization of cold rolled 6016 aluminum alloy sheets is very fast, which can be completed within 1.4min during solution treatment at 550℃, the orientation and size of recrystallization grains have little changes when the solution time prolonged up to 15min;(2)There are insoluble phases Al2Fe3Si3 and soluble phases Al1.9CuMg4.1Si3.3, Al0.56Mg0.44, and Mg2Si in as cold rolled 6016 aluminum alloy sheets. When the solution time is more than 5min, soluble phases were already dissolved completely and the strength, hardness, elongation and n, r value of 6016 aluminum alloy sheets didn’t change much. The property of 6016 aluminum alloy sheets after water cooling is better than after air cooling;(3)It can be found that the shorter the stand-to time after solution treatment at RT before pre-aging is, the more effectual is the pre-aging treatment on improving the formability and bake-hardening of 6016 aluminum alloy sheets;(4)For 6016 aluminum alloy sheets, when the stand-to time at RT after quenching is 5min, the optimal pre-aging condition is pre-aging at 160℃ for lOmin, and ReL, Rm, A, IE, n, r15 of aluminum alloy sheets after pre-aging treatment are 116MPa,235MPa,26%,8.12mm,0.28 and 0.78, respectively, and ReL of alloy sheets increases to 254MPa after paint baking at 175℃ for 30min;(5)For 6016 aluminum alloy sheets, when the stand-to time at RT after quenching is 60min, the optimal pre-aging condition is pre-aging at 180℃ for 10min, and ReL, Rm, A, IE, n, r15 of aluminum alloy sheets after pre-aging treatment are 129MPa,245MPa,28%,7.94mm, 0.25 and 0.75, respectively, and ReL of alloy sheets increases to 186MPa after paint baking at 175℃ for 30min.