Effect of strontium modifier on the microstructure, mechanical properties and fractography analysis of as-cast Al-Si7Mg0.3 alloy

Abstract

ABSTRACT Al-Si7Mg0.3 (LM25/A356) alloy is mainly used in cast form and the microstructure of LM25 alloy mainly depends on the rate of solidification and composition of modifiers. This study explores the influence of the strontium modifier on the microstructural changes, mechanical properties and fractography analysis of the Al-Si7Mg0.3 (LM25) alloy. Optical microscopy (OM), scanning electron microscopy (SEM) and X-Ray Diffraction (XRD) analysis were performed on the LM 25- x% Sr (x = 0.01, 0.02, 0.03, 0.04 and 0.05) specimens to study the grain refinement, modifier distribution and elemental peaks in the as-cast samples. Experimental results concluded that the agglomeration generated at the 0.05 % Sr modifier added with LM25 alloy and the elements corresponding to this agglomeration was confirmed as strontium oxide (SrO) by using JCPDS file numbers. The maximum ultimate tensile strength of 173 MPa, yield strength of 132MPa and hardness of 103 VHN were obtained at 0.04 % strontium added LM 25 alloy. The ductile fracture was confirmed based on the dimples generation on the fractured layer of 0.01 %, 0.02 % and 0.03 % Sr added LM 25 alloy and the fracture mechanism was changed to brittle mode with the addition of 0.04 % and 0.05 % Sr.