Effects of Fe content on microstructural and mechanical wear properties in innovative aluminium alloys for piston applications in the automotive sector

The main goal of this study is to identify the effect of Fe content on microstructural and mechanical wear properties in aluminium alloys used in the automotive sector, specifically for pistons. The alloys analysed are EN AB-46000 (AlSi9Cu3(Fe)) with two different Fe wt.%: 0.722% e 1.223%; from now on, the alloys will be appointed to, respectively, as low-Fe and high-Fe alloy. Along with Fe wt.%, different casting temperatures are taken into account as well, in a range from 680°C up to 1030°C, with 70°C of difference between every temperature. Wear test, hardness test and microstructural analysis are done on each sample, one for every temperature, to determine the mechanical and metallographic properties of both alloys. The influence on the test results of both iron amount and casting temperature is considered. Moreover, the formation conditions for -phase and -phase (two Fe-rich compounds) are determined, again as function of casting temperature and Fe wt.%, with the target of obtaining an alloy with the least possible amount of -phase, which is deleterious for the component performances. The final objective is to determine two equations, one for hardness and one for wear rate, as functions of casting temperature and Fe wt.%. The aim of chapter 1 is to gather literature concerning the subject of the thesis, then in chapter 2 the design of experiment is done, identifying the chemical compositions of the two alloys and defining the casting temperature and cooling rate. Chapter 3 describes the process followed for the preparation of the samples that will undergo the experimental procedure, which is described in chapter 4, along with the data analysis, the retrieved considerations and empiric equations. From the iron analysis the -phase morphology varies as the bath temperature increases, in particular at higher temperatures it assumes a chinese-script form, while at lower ones it assumes a more polyhedral form. It is also found that -phase decreases its quantity with the increase of the bath temperature. As shown in the data, it seems that high Fe content is detrimental for hardness and wear resistance. If hardness and wear resistance are requested, the evidence of the data obtained suggests that the low-Fe alloy at a casting temperature of 820 °C results to be the best solution from an economical and performance perspective.