Study of a Formability Process Chain for a Copper-Free Al-Zn-Mg-Alloy by a Retrogression and Re-Aging Treatment (RRA)

Abstract

The material for the experiment was a copper-free Al-Zn-Mg-alloy. Because of natural aging after solution treating these materials are not storable at room temperature in T4 temper. Therefore 7xxx series Al alloys are mainly delivered in an artificially aged T6 temper. This state is not proper for a cold formability process, a thermal formability processes like hot working has to be use. In this paper a process chain based on so-called retrogression and re-aging (RRA) treatment was investigated to allow cold forming after a short time treatment. To achieve this tensile test specimens were tested under various retrogression temperatures (220 - 360 °C) and at times (1 - 7 min) to evaluate the flow curve. The properties like strain hardening exponent n and strength coefficient C of the Ludwik-Hollomon equation, a common approximation of the flow curve, are illustrated and the influence of the process parameter is discussed. A re-aging treatment at 130 °C for 16 h after retrogression of non-deformed and deformed material is also examined.