Fast light alloy stamping technology (FAST) for manufacturing lightweight pressings from dissimilar aluminium alloy-tailor welded blanks

Abstract

Dissimilar aluminium alloy-tailor weld blanks (DA-TWB) are increasingly being used in transportation industries due to their significant benefit in reinforcing vehicle structures as well as improving lightweight performance. Hot stamping technologies enabling the manufacture of lightweight pressings from DA-TWB have yet to be developed and be widely implemented. In the present research, a unified automated production system was developed to integrate the functions of heating, blank transfer, forming and post-form heat treatment, and automatically conduct hot stamping of materials under various conditions with high accuracy, enabling a forming temperature of up to 650 °C, a heating rate of up to 200 °C/s, a blank transfer speed of up to 200 mm/s, a forming speed of up to 1500 mm/s and a die closing force of up to 50 kN. The effects of processing parameters, including heating rate ranging from 1 to 150 °C/s, forming temperature ranging from 200 to 500 °C and forming speed ranging from 50 to 350 mm/s, on the post-form hardness/strength, microstructure and springback of individual AA6082 and AA7075 aluminium alloys were subsequently studied to obtain an optimised processing window for forming the DA-TWB joined by friction stir welding, which was formed by using the developed production system. From the studies, 95 % of the T6 temper's hardness was achieved and metastable strengthening phases were dispersedly distributed in both alloys (i.e. β″ for AA6082 and η′ for AA7075) with negligible springback of less than 2° by using a heating rate of 50 °C/s, a forming temperature of 300 °C and a forming speed of more than 250 mm/s. In addition, the forming process of the DA-TWB was finite element simulated for thermal and mechanical analysis. It was validated that Fast light Alloy Stamping Technology (FAST) with an optimised processing window was capable of providing superior strength-springback behaviour at a production cycle time of less than 10 s.