Feasibility study on contact heating warm forming of 7075-T6 aluminum alloy

7075 aluminum alloy is becoming an ideal material for the manufacture of vehicle body parts due to the demands for energy-saving and lighter vehicles. To solve the problem that the strength of 7075-T6 aluminum alloy decreases due to over-aging after warm forming, contact heating warm forming (CHWF) technology was proposed in this work. Contact heating is a fast and efficient heating method that can make the blank reach the target temperature in a very short time. In this work, the effect of contact heating on the mechanical properties and microstructures of 7075-T6 aluminum alloy after warm forming and paint-baking (PB) was studied. It only took about 11.5 s to heat the 2 mm 7075 aluminum alloy sheet to 200 celcius by contact heating, and the strength and the hardness of the formed parts could reach 94% and 92.5% of T6 condition, respectively. In contrast, the heating furnace needed 690 s to heat the sheet to 200 & DEG;C, and the strength and the hardness of the formed parts were 87% and 85.4% of T6 condition, respectively. Due to the fast heating rate of contact heating (17.5 celcius/s), the atoms and vacancies in the matrix did not have time to undergo diffusion and aggregation, so that the precipitates could not coarsen obviously. As a result, most of the & eta;' precipitates in the T6 condition were retained. However, long-term heating in the furnace led to the transformation of & eta;' precipitates into coarse & eta; phase and the loss of strength and hardness.