Effect of Ca Impurity on Microstructures and Mechanical Properties of As-Cast Al-5Mg Filler Alloy

Effects of Ca impurity on microstructures and mechanical properties of Al-5Mg filler alloys were investigated with SEM, EDS, XRD, tensile test and impact test. The results indicate that the phase composition of Al-5Mg alloy is affected by the Ca impurity. It is observed that block-like (Ti,Cr)(2)Ca(Al,Mg)(20) phase is distributed discontinuously along the grain boundaries when the content of Ca is less than 0.28 wt%. When the content of Ca is over 0.28 wt%, bar-like Al2Ca and block-like (Ti,Cr)(2)Ca(Al,Mg)(20) combine together and are distributed along the grain boundaries, and the amount and size of Ca-rich phase (both the bar-like and block-like) increase with the increasing of Ca content. Tensile strength of the Al-5Mg alloys increases firstly and then decreases with the increasing Ca content, and the tensile strength gets to a maximum value when the content of Ca is 0.28 wt%. The plasticity and fracture toughness decrease slowly (Ca content 0 wt%similar to 0.28 wt%) but then significantly decrease (Ca content>0.28 wt%), and the tensile or impact fracture mode transform from the transgranular ductile fracture to brittle cleavage fracture.