A356 Al alloy containing 7% Si and 0.3% Mg is widely used in automobile and aircraft industries due to excellent castability, good corrosion resistance and good pressure tightness. The present investigation was undertaken to explore the possibilities of rare earth metal additions primarily as modifiers of eutectic silicon and secondarily beneficial alloying element. In the present study, the effect of rare earth addition and stirring on the mechanical properties of a cast A356 alloy was studied. Alloy was casted by addition of 0%, 0.5 wt%, 1.5 wt% rare earth along with 0, 400 and 600 rpm of stirring speed. Microstructural characterization of the casted A356 alloy was carried out by means of Optical Microscopy and its phases were detected by XRD. Mechanical characterization was based on tensile and hardness tests. Inclusion of rare earth along with stirring gives grain refinement and increases the strength of the as-cast alloy. Optimal rare earth addition was found to be 0.5% at 600 rpm of stirring speed. Addition of rare earth causes formation of intermetallic compound as observed in XRD and stirring results in size reduction of dendrites and desegregation of Si needles present in A356 alloy.

The increasing need for lighter and safer cars is the driving force behind the research in the area of high strength light metal safety part applications (Menghani and Joshi, 2006). Aluminum A356 (Al 7 wt%-0.3% Mg) alloy is one of the widely used casting aluminum alloys because of its good mechanical strength, ductility, hardness, fatigue strength, pressure tightness, fluidity and machinability. In unmodified A356 alloy, the main eutectic reaction occurs at 574 °C as a binary reaction, which results in coarse irregular plate like silicon. The needles act as crack initiators and weaken the mechanical properties significantly. The modification of eutectic silicon is of general interest since fine eutectic silicon along with fine primary aluminum grains improve mechanical properties and ductility. Modification treatment consists of addition of a ‘modifier’ such as strontium (Sr) or sodium (Na), whereby the naturally occurring acicular form of the eutectic silicon is converted to ‘modified’ or a fibrous form which is beneficial to the alloy properties, in particular, the ductility (Sharan and Anantharaman, 1967; Ravi et al., 2002; Jian et al., 2006; and Sebaie et al., 2008).

Mechanical Engineering Journal, A356, Rare earth, Gravity die casting, Grain refinement, XRD.