Microstructure and Corrosion Behaviour of A356 Al-Si Alloy and its Friction Stir Welds

摘要

Friction stir welding (FSW), a promising solid state joining process developed especially to overcome the problems associated in fusion welding of aluminium alloys. Pressure die cast A356 Al-Si alloy with strontium modification in T6 and as cast condition was joined by the FSW process. The microstructural changes in nugget zone (NZ), heat affected zone (HAZ) and thermomechanically affected zone (TMAZ) were studied. Corrosion resistance of the weld joint is related to prior thermal condition of the alloy and microstructural changes taking place at various zones during the FSW process. In the present work effect of prior thermal condition of the base metal on microstructure and corrosion resistance of A356 alloy was studied. Corrosion behaviour of base metal and welds was studied using potentiodynamic polarization testing. Hardness profile across the weld indicated the softening of TMAZ. This is attributed to the possible coarsening of dispersoids. Corrosion resistance of the nugget was found to be better than that of TMAZ, HAZ and base metal which attributes the uniform distribution of fine disintegrated eutectics at high rotational speeds associated in the welding process in both the conditions of the alloy.