SCANNING ELECTRON MICROSCOPY IDENTIFICATION OF INTERMETALLIC PHASES IN Al-Si CAST ALLOYS

Abstract

Al-alloys are preferred in the automotive industry because of theirs lightweight. European Union has on the present big interest of share recycling aluminium, and so increase interest about recycled (secondary) aluminium alloys and castings from them. Recycled aluminium alloys are made out of aluminium scrap and workable aluminium garbage by recycling. Due to the increasing production of recycled aluminium cast alloys is necessary their strict metallurgical control. The mechanical properties and the microstructure are dependent on the composition, melt treatment conditions, solidification rate, casting process and the applied thermal treatment. The mechanical properties depend, besides the morphologies, type and distribution of Si, Cu, Mg and Fe-phases, on the grain size, DAS, porosity distribution or profile. Therefore, study the microstructure of Al alloys is very important. Analysis of microstructure in the AlSi9Cu3 alloy was performed on the SEM. For study and identification of intermetallic phases’ was utilized standard (Dix-Keller, 0.5% HF) and deep etching. Deep etching consists of dissolving the alpha-matrix in the reagent (30 s in HCl) in order to reveal the three-dimensional morphology of the silicon particles and intermetallic phases. For elemental composition of the specimen were used x-rays analysis (line, point and surface - mapping). Finally the fracture surfaces of Al-Si alloy after impact test in the as-cast state were observed.