Synergistic improvement in bake-hardening response and natural aging stability of Al-Mg-Si-Cu-Zn alloys via non-isothermal pre-aging treatment

Journal article (2022)

Authors

G. Li Team Maria Santofimia Navarro - Mechanical, Maritime and Materials Engineering , University of Science and Technology Beijing
Mingxing Guo University of Science and Technology Beijing
Jinqing Du University of Science and Technology Beijing
Linzhong Zhuang University of Science and Technology Beijing
Research Group
Team Maria Santofimia Navarro (Mechanical, Maritime and Materials Engineering) (TU Delft)
Copyright: © 2022 G. Li, Mingxing Guo, Jinqing Du, Linzhong Zhuang
DOI: https://doi.org/10.1016/j.matdes.2022.110714
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Published Date

2022

Language

English

Faculty

Mechanical, Maritime and Materials Engineering

Department

Materials Science and Engineering

Research Group

Team Maria Santofimia Navarro

Abstract

A new non-isothermal pre-aging treatment was proposed and utilized in Al-Mg-Si-Cu-Zn alloys, together with natural aging and artificial aging. The influence of cooling rates on subsequent precipitation behaviors was investigated by experimental and thermodynamic simulations. The results show that by controlling the formation of clusters/GP zones through changing pre-aging cooling rates, i.e. PA-0.2, PA-0.3 and PA-0.4 (°C/min, from 80 °C to 40 °C), an excellent bake hardening increment and natural aging stability can be obtained. The highest bake hardening increment can reach 180 MPa for PA-0.4 sample, which is twice higher than those of Al-Mg-Si-(Cu) alloys. The microhardness remains almost unchanged within NA for 14 days at a lower level of approximately 85 HV0.2. Thermodynamic simulations estimate the solvus temperatures and chemical composition for GP zones, revealing the strengthening and stabilising mechanisms behind: a) Mg-Zn- clusters formed during pre-aging can suppress Mg-Si- clusters formation in the natural aging process, b) non-isothermal hinders the precipitates growth, a faster cooling rate leads to smaller and softer Mg-Zn- clusters, and c) the formation of a heterogeneous microstructure contributes to the high bake-hardening response without changing the type of strengthening phase β″. Finally, the clustering and aging process was illustrated and explained.