Effect of solid solution phase constitution on dissimilar Al/Cu FSW using Zn as an alloying element at the joint interface

Abstract

The effect of Al/Zn/Cu binary and ternary solid solution phase constituents on metallurgical and mechanical properties of Al/Cu dissimilar friction stir welding using Zn as an alloying element was investigated. Because of Zn interlayer material binary intermetallic compounds (IMCs) such as AlCu, Al2Cu, Al.71Zn.29, CuZn5 and ternary IMCs such as Al4.2Cu3.2Zn.7 are formed. These solid solution alloying phase constituents improved the weld properties of the joint. The tensile strength was enhanced by 13% for Zn alloying specimens compared with non-alloyed weld specimen and 104% of the Al base material due to the formation of thin and controlled IMCs and solid solution phase constitution strengthening as well as Orowan strengthening. The fractured surface with Zn alloying element suggested combination of ductile–brittle fracture and indicated transgranular failure. Micro-hardness with Zn alloying specimen is higher compared to the non-alloyed specimen for the existence of different IMCs at the stir-zone. The mapping analysis indicated that the thickness of the IMCs with Zn alloying was at micro-meter level. Phase constituent revealed that thin continuous and uniformly distributed binary and ternary phases are beneficial for the enhancement of mechanical and metallurgical qualities. Macrostructural views revealed variation in IMCs flows at non-alloyed and Zn alloying cases. Different weld zone reflected grain variations and finer grain at the weld nugget due to the nucleating effect of Zn interlayer.