Recycling and Degassing of AZ91E Magnesium Alloy Castings and Its Effects on Mechanical Properties and Microstructure

The objective of this study was to examine the effects of filters and a hexachloroethane degasser on the microstructure and mechanical properties of recycled AZ91E magnesium alloy castings. This research is important as it will allow an increased use of recycled metal, thus reducing the costs of magnesium castings. The AZ91E castings were produced using a H13 tool steel mold machined to American Society for Testing and Materials (ASTM) B108-06 standards. Casting conditions examined included no filter, filter, filter + 1 remelt, filter + 2 remelts and finally, filter + 2 remelts + 1 wt.% Ashbury 751 degasser. The mold and pouring temperatures were 475 and 720C (887 and 1328F), respectively. Without a filter, the average yield strength, tensile strength and elongation of the AZ91E alloy casting were 93 MPa, 155 MPa and 2.26 %, respectively and with a filter increased to 97 MPa, 167 MPa and 3.18 %, respectively. The highest average elongation was 4% for the AZ91E + filter + 2 remelt + 1wt.% degasser casting. The remelting of castings caused increased scatter in mechanical properties and resulted in Mg-Al based oxides on the fracture surfaces which bonded poorly with the matrix causing premature fracture. The results emphasized the importance of investigating the recycling of magnesium castings to promote their use in aerospace and automobile applications. A better understanding of the formation, behavior and removal of inclusions in magnesium melts will improve the quality of magnesium castings.