Tungsten Laser Alloying of A356 Al Alloy - Tribological Performance and Characterisation

Abstract

In the present work, sand cast Al alloy A356 was laser alloyed with tungsten using a two stage technique of laser alloying. A continuous wave, fibre optically delivered, Nd-YAG laser was employed for alloying the tungsten powder, and the coatings were produced by varying beam interaction with the substrate by altering the traverse laser velocity. Characterisation of the laser treated alloy was performed by various techniques. Optical (OM) and scanning electron microscopy (SEM) were used to examine the morphology and microstructure of the specimen surfaces and cross-sections. Surface layers alloyed with tungsten contained relatively large amounts of intermetallic compounds such as Ti₅Si₄, Mg₂Si, Al₅ W, Al₁₂W, and Al_3·21Si_0·47 identified by X-ray diffraction. Friction and wear tests were carried out on all specimens by using a ball on disc tribometer under dry conditions. The static partners were balls of 6 mm diameter made of WC + 6%Co. It was determined that the laser treated surfaces presented an increase in wear resistance between 40% and nearly 110% when compared to the wear resistance of the untreated Al alloy, and the improvement was proportional with the laser beam- substrate interaction time.