Self hardening aluminum alloys for automotive applications

Self-hardening aluminum alloys (Al-Zn-Si-Mg alloys) represent an innovative class of light aluminum alloys. They present high mechanical properties, which make them suitable for many applications in different industrial fields, especially in transport industry. The most important and relevant feature of the self-hardening alloys is related to their good performance, without the need of any heat treatment: they are subjected to a natural ageing phenomenon at room temperature after a storage period of about 7-10 days. The possibility to avoid the heat treatment represents an important benefit, contributing to considerably reduce both the production cost of some components and the amount of energy involved in the manufacturing process. Furthermore, without heat treatment the risk of component's deformation during the production is eliminated. The goal of this PhD Thesis was to find an alternative solution to the actually used T6 heat-treated A356 alloy for automotive component production. The feasibility of the development, of a knuckle suspension component, starting from the self hardening alloy was evaluated and investigated. In addition, some qualitative and semi-quantitative considerations was figured out from economical point of view. The use of the self-hardening aluminum alloy allows avoiding any heat treatment, consequently an important energy saving can be reached during the manufacturing, especially in terms of gas and electricity consumption, that are important features for the environment. A consistent part of this thesis was focalized on the study of the structural features and mechanical properties of the self-hardening aluminum alloys. Another part was dedicated to investigate their corrosion resistance. The effect of the Mg content and of the cooling rate, on the microstructure of three different self-hardening aluminum alloys, were investigated, aiming to define the optimal alloy composition for knuckle suspension component production.