Two step–ageing of 7xxx series alloys with an intermediate warm-forming step

A Materials Science-Based Approach to Finite Element Simulation of Warm-Forming of Al-Mg-Zn Alloys

“…7021+ achieved 92 and 95 % of T6 yield strength (442 MPa) for paint-bake and short-T6, respectively. It was found by transmission electron microscopy that paint-bake results in a coarser structure of hardening Mg-Zn-precipitates than the short-T6 regime, which in turn creates coarser precipitates than a standard T6 treatment [1]. Our results indicate that both alloys are well-suited for the warmforming process combined with the short-T6 treatment, while Alclad 7075 shows better paint-paint response.…”

“…Deep-drawing and heat treatment. Long octagonal blanks (dimensions given in [1]) were cut. Solution heat treatment (SHT) was performed by placing the blanks in a pre-heated oven (AA7075: 480 °C, 25 min; AA7021+: 515 °C, 15 min) followed by quenching in water.…”

“…Punch and die were also pre-heated to the desired temperature. A drawing of the long cup tool and additional information are given in [1]. The blank holder was closed with 50 kN (~25 bar) and after 30 s, deepdrawing was started (20 mm/s) to a draw depth of ~50 mm.…”

“…7021+ is a non-standard alloy based on AA7021 with increased Mg and Zn levels. The chemical compositions are reported in [1].…”

“…Automakers aiming to reduce vehicle weight and aircraft industry striving to cut production costs in the wake of the Covid-19 crisis require economical sheet metal forming processes for Al-Zn-Mg(-Cu) alloys (7xxx series). We have shown recently [1,2] that warm-forming of under-aged (pre-aged) blanks is a process with distinct advantages over other approaches, including:…”