Investigation On Warm Forming Of 7075-T6 Aluminum Alloy

In recent years, with the vigorous development of the automobile manufacturing industry and a substantial increase of car ownership, which will inevitably lead to reducion of oil energy and deterioration of environmental quality. Lightweight of automobile is an effective measure to reach "lossing weight, reducing emission, safety, green". The use of lightweight materials has become a major approach to achieve lightweight automobile. Because of 7xxx series aluminum alloy have low density, high strength and other unique excellent properties, which has becomed potential materials to manufacture high strength automotive parts.It is pointed out that the basic mechanical properties of aluminum alloys provide an important basis for the study on the formability of aluminum alloy. In this paper, the 7075-T6 aluminum alloy sheet was studied by uniaxial tension test to master the basic mechanical properties, the true stress-strain curves were obtained. The study showed that: increasing temperature and decreasing strain rate would help to improve the formability of 7075-T6 aluminum alloy sheet.In order to research warm forming process of 7075-T6 aluminum alloy sheet, we had designed a set of warm forming die device. By using this device, the isothermal and gradient of two kinds of warm forming processes were studied firstly, then the influence of forming process parameters on the forming performance was analyzed, At last, the mechanical properties of the parts after forming were studied. Through the research results:(1) In isothermal forming process, the drawing limit ratio(LDR) of 7075-T6 aluminum alloy sheet increased firstly and then decreased while raising temperature, the maximum of LDR reached 2.1, it could basically meet the forming of some automobile structural parts. In order to further improve the forming limit of sheet metal so that a new gradient forming process was putted forward. The LDR of aluminum alloy sheet was raising while raising temperature and the maximum of LDR reached 2.25.(2) The influence of parameters on the warm drawing of 7075 aluminum alloy sheet was also researched. The results showed that the optimum temperature of die and blank holder was 180~200 ℃, while that of punch is 60~90 ℃; holding time required 15 s at least; blank space was 1.05~1.10t; PTFE was used as lubricant and while drawing, the drawing rate was in the range of 5~10 mm/s.(3)The hardness testing of the original blank, the forming parts and the forming parts after the baking process were carried out. Compared with the original blank hardness, the hardness of the side wall of the formed part was decreased After baking the forming parts, The hardness curve was more smooth than before baking, and there was a certain degree of improvement, but still lower than the original blank hardness.