Abstract

The purpose of this research is to investigate the influence of Manganese (Mn) on cast aluminum alloys where a substantial amount of Iron (Fe) is included. Ductility and tensile strength need to be improved in recycled aluminum alloys where greater amounts of Fe are found. Fe is a common impurity and is known to be detrimental to mechanical properties and in order to neutralize the effects of Fe; modifiers such as Mn are added. In this investigation, attempts will be carried out aiming to find the optimal amount of Mn. Other related topics that will be discussed are whether there exists a Mn/Fe ratio which clearly modifies the harmful iron- rich phases and improves the properties for a certain alloy or not. Also, will the heat treatment have a significant effect on mechanical properties? These are some of the questions that will be answered in this paper.

It is hard to find research articles that focus only on the influence of Mn on the microstructure and mechanical properties of Al-Si cast alloys. Much of the work that is already published concerns only a specific alloy and casting method. In this work three different casting processes, sand-, die- and high pressure die-casting, will be simulated by using gradient solidification equipment. Furthermore, the influence of heat treatment on the mechanical properties will be examined.

The results showed that the solidification rate had the biggest impact on the microstructure and mechanical properties of the alloys, where the fastest cooling rate gave the best results. The effect of Mn seems to influence the samples with coarser microstructures significantly where it had time to modify the Iron-rich needles, also called the β-phase. At higher cooling rates the impact of Mn was impeded. It has been observed that a high content of Mn (around 0.6%) needs to be added before the properties start to improve. UTS (Ultimate Tensile Strength) and YS (Yield Strength) are improved while ductility is lowered. Heat treatment did not seem to have any influence on the effects of Mn.