Design and characterization of a novel MgAlZnCuMn low melting point light weight high entropy alloy (LMLW-HEA)

Abstract

Development of high-entropy alloys (HEAs) is one of the remarkable advancements in the progress of new materials. In recent years, continuous efforts have been made to design light weight high-entropy alloys (LWHEAs) with suitable microstructure and superior properties. This paper reports the preliminary results of a study aimed at design and development of a new low melting point LWHEA (LMLW-HEA) based on AlMgZnCuMn alloy system without excessive intermetallic compounds formation. In this research, first, the initial chemical composition of the alloy was designed according to thermodynamic parameters, and then the alloy was melted in a resistance electric furnace. Since the thermodynamic indicators have been defined based on alloys containing 3d transition elements, formation of binary intermetallic compounds was predicted with the help of Midema model. To investigate the effects of cooling rate and heat treatment on the structure of the designed alloy, the molten alloy was poured into two different molds made of silica sand and steel, and both as cast samples were also heat treated. Microstructural features, mechanical properties and thermal stability of the samples were then examined. Density of the samples was measured to be less than 3.4 gr/cm3 which was very close to the theoretical density of the alloy. Structures of all the samples were complex and multi-phase and contained intermetallic (ordered solid solution) binary and ternary compounds including Mg7Zn3, MgZn2, Cu2Mg, Al2Cu, Mg32 (Al, Zn)49, Mg32Cu7Al47, Al25Mg37.5Zn37.5, and CuMgZn phases. The designed alloy was brittle under all the processing conditions. Compressive strength of the alloy reached to about 95 MPa, and its hardness was in the range of 110–120 HV. Oxidation resistance of the alloy was evaluated at a temperature about 30 °C below its solidus temperature and no weight change was observed in the sample after 14 h. It is suggested that the designed alloy is a suitable candidate for high temperature applications not involving impact or cyclic loading.