SOME STUDIES ON DEVELOPMENT OF DUCTILE CONVENTIONAL CASE MAGNESIUM BASED ALLOYS

Abstract

Magnesium-based alloys have enormous potential for high performance structural applications due to their light weight combine with high specific strength, superior damping capacity, etc. Based on these superior properties and a combinative requirement for reducing environmental burdens by using light weighted stuructures, the research and development of magnesium alloys for practical industrial application have overwhelmingly increased worldwide during the past decade. AZ series cast Mg alloys have been extensively studied and used for some structural components of automobiles, aircraft, and computers. Alloying elements are partly present in solid solution, partly as intermetallic constituents. It is, however, interesting to see that there is a fairly good correlation between strength and total wt% of added elements. An effort has been made to develop a new Mg-alloy system that possesses exceptionally high ductility as well as good mechanical strength at room temperature in as-cast state. A novel Mg alloy system contains small amount of Al, Zn, Sn, Pb, Si and Misch metal (MM) has been developed for easy mechanical forming at room temperature .These are low-cost Mg alloys with improved tensile strength. The main alloy elements in the novel alloy system Sn and Pb are not expensive and the other alloy elements are either cheap and/or used in small amounts. Therefore, this new Mg alloy system is not expensive and may be produced at a large scale for a wide range of industrial applications. Microstructure evolution and resulting mechanical properties in Mg-Al-Zn-Pb-Sn based alloys have been investigated. The microstructure of the studies alloys Mg-4Al-3Zn-3Sn-3Pb and Mg-4Al-3Zn-3Sn-3Pb-0.5misch metal ( MM) are dendritic in nature while for Mg-3Zn-3Sn-3Pb-2Si the ‘Chinese script’ Mg2Si intermetallic structure is obtained. Effect of MM on microstructure and mechanical properties as-cast Mg-4Al- 3Zn-3Sn-3Pb-0.5MM is maximum. The result shows that MM addition leads to obvious grain refinement. The UTS, YS, and percentage elongation of Mg-4Al-3Zn-3Sn-3Pb-0.5MM alloy are 170, 44 and 3.4%. The alloys investigated exhibit plastic deformation and work hardening during wear test. Specific wear rate (mm3/N-m) or cumulative wear loss (mm3) is found maximum for Mg-4Al-3Zn-3Sn- 3Pb-0.5MM. Addition of 4% Al, 3% Pb, 3%Sn, 3% Zn and 3% Si leads to Al-Sn, Al-Pb, Pb-Zn, phase in α-Mg matrix grains. The effects of alloying elements on Vickers hardness of alloys were examined. The vicker hardness value is found maximum for Mg-3Zn-3Sn-3Pb-2Si is 61 HV. The fracture surface of of Mg-Al-Zn-Sn-Pb alloys based system shows clearly ductile fracture evidence.