Effect of temperatures and pulling rates on microstructure and mechanical properties of 6061 aluminum alloy in directional solidification

Abstract

During directional solidification, temperatures and pulling rates have significant influences on microstructure of casting rods. And, mechanical properties of 6061 aluminum alloy rods depend on microstructure formed in the directional solidification. In order to study the effect of temperatures and pulling rates on microstructure and mechanical properties, the directional solidification experiment of6061 aluminum alloy were performed using Bridgman-type vacuum furnace with liquid metal cooling(LMC) method at different temperatures (700 °C, 750 °C and 800 °C) and pulling rates (20 μm/s, 50 μm/s, 100 μm/s and 150 μm/s). Microstructural investigation of 6061 aluminum alloy rods was performed using Hitachi SU8070 SEM. And, tensile tests and microhardness tests were conducted on JVJ–50s test machine and MHVD-1000IS hardness tester separately. Experimental results indicate that the dendritic structure of the specimen gradually is refined uniformly, and the intergranular spacing becomes smaller with the increase of temperatures. Some defects lead to the decline of mechanical properties of alloy with the increase of temperatures. The tensile strength at the temperature of 750 °C is the highest, reaching 182.51 MPa. However, the microhardness at the temperature of 800 °C is the highest, reaching 56.77 HV. When the pulling rate is 50 μm/s, the tensile strength shows better than that at the pulling rate of 100 μm/s and 150 μm/s, reaching 183.31 MPa. However, the highest microhardness takes places at the pulling rate of 150 μm/s, reaching 67.66 HV.

DOI: http://dx.doi.org/10.5755/j01.mech.24.1.19499