Grain refinement, Microstructural characterization, and tensile properties of die-cast AZ91 alloy via Lead and Tin additions

Effects of different amounts of lead (Pb) and tin (Sn) on microstructure and tensile properties of the AZ91 alloy were studied. The results presented that the microstructure of AZ91 alloy is consisted the α-Mg phase and semi-continuous network of β-Mg17Al12 intermetallics. For the as-cast AZ91 alloy, the average grain siz and the β phase volume fraction were 96.2 µm and of 25.3%, respectively. By adding 1 wt.% Pb and 0.5 wt.% Sn, the lowest grain size and volume fraction values obtained. Exceeding Pb and Sn additions have been led to the increasing of the grain size. Furthermore, Sn additions formed the Mg2Sn intermetallic, while Pb additions didn’t form any obvious intermetallics. The Ultimate Tensile Strength (UTS) and tensile elongation (%El) values of the cast AZ91 alloy were 129 MPa and 2.7%, respectively. The optimum amounts of UTS and %El values were achieved by adding 1 wt.% Pb and 0.5 wt.% Sn, respectively. More Pb and Sn additions deteriorated the tensile properties. The fracture surface observations showed that fracture mode in the cast AZ91 alloy was cleavage. Moreover, 1 wt,% Pb and 0.5 wt.% Sn additions altered the fracture mode to more quasi-cleavage fracture.