Ageing Behaviour of Al-Mg-Si Alloys After Cryogenic and Room Temperature Deformation.

Belinda Gruber,Stefan Pogatscher,Peter J Uggowitzer,Alexander Schökel,Werner Fragner,Florian Grabner,Florian Spieckermann

doi:10.3390/ma13030554

Abstract

The aim of this study is to investigate the effects of cryogenic and room temperature pre-deformation on subsequent artificial ageing of Al–Mg–Si alloys. Naturally aged and pre-aged samples were strained to 5%, 10% and 20% at RT (25 °C) and under liquid nitrogen, and artificially aged at 185 °C. Pre-deformation generally increases ageing kinetics for both the naturally aged and pre-aged alloys, which increase in proportion to the degree of pre-deformation, and which are slightly more pronounced for the cryogenic condition. The peak strength is constant, except for when a low degree of pre-deformation is used, in which case it is slightly reduced. Cryogenically deformed samples show an increased strength and hardness, compared to samples pre-deformed at RT, when subjected to an equal magnitude of strain. This difference is reduced during artificial ageing. Synchrotron measurements reveal that this behaviour can be linked to the greater dislocation density, which is not completely recovered even after prolonged ageing at 185 °C.

Highlights

In the automotive industry, Al–Mg–Si alloys are preferably used as lightweight material due to their advantageous mechanical properties, such as good corrosion resistance, weldability, and great strength [1,2]
During the pre-ageing heat treatment, the first nuclei for the artificial ageing are formed, and a formation of natural ageing phases during RT storage is suppressed for a certain time, leading to a more pronounced artificial ageing response [10,11]
Aged (T4) and pre-aged (PA) samples of alloy EN AW 6016 were strained to 5%, 10% and 20%

Summary

Introduction

Al–Mg–Si alloys are preferably used as lightweight material due to their advantageous mechanical properties, such as good corrosion resistance, weldability, and great strength [1,2]. Schneider et al [6] identified an increase in uniform elongation of 42% in alloy AA 6016 when the temperature was lowered to. Industrial deep drawing processes can be carried out at cryogenic temperatures with the advantage of affording greater freedom when it comes to design. In the automotive industry, during the manufacturing of outer sheet panels, an additional heat treatment is applied. This heat treatment is applied after the last deformation step (deep drawing) and Materials 2020, 13, 554; doi:10.3390/ma13030554 www.mdpi.com/journal/materials

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