Investigation of microstructure, hardness, corrosion and machinability properties of commercially pure aluminum alloyed with rare-earth elements

Abstract

In this study, three different rare-earth elements, namely gadolinium (Gd), yttrium (Y) and neodymium (Nd), were added to commercially produced Al99.8 aluminum at various weight ratios (0.1%, 0.2% and 0.3%). Since rare-earth elements were added as a magnesium-based master alloy, commercial Al99.8 alloy containing 0.7 wt% Mg was also cast in the experimental study to investigate the effect of magnesium added to the alloy. The effects of rare-earth elements added to commercially pure Al99.8 aluminum on the microstructure, hardness and electrochemical corrosion behavior in 3.5% NaCl environment in the casting position of the alloys were investigated. In addition, the samples of the alloys were drilled with a spindle speed of 4000 rpm and a feed rate of 200 mm/min and the effects of rare-earth elements on thrust force, burr and surface morphology were investigated. It was observed that intermetallic compounds containing these elements were formed in the microstructures of the casting alloys to which rare-earth elements were added, the microstructure generally became thinner depending on the added ratios, the grain structure changed from columnar to equiaxed and microsegregation was eliminated compared to the alloy containing Mg. In electrochemical corrosion tests, the worst corrosion resistance was found in the alloy containing Mg, while the Icor values indicating the corrosion rate were found to increase with the addition of Gd, Y and Nd, respectively, compared to the Al99.8 sample. Scanning electron microscope examinations of corroded surfaces showed that the alloys started to dissolve from the intermetallic compound and matrix interface. While the corrosion mechanism was seen to be pitting corrosion in the alloy containing Mg, the mechanism was found to be microgalvanic corrosion in the alloys containing rare-earth elements. When the samples containing rare-earth elements were drilled, less thrust force was generated compared to Al99.8 aluminum. The highest amount of burr was generated in the Al99.8 sample. In addition, better surface quality was obtained when the samples were drilled by adding rare-earth elements.