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

Tao He,Hong Jun Liu,Yuan Ming Huo,Xiao Jie Yi,Li Min

doi:10.5755/j01.mech.24.1.19499

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

Highlights

As Al-Mg-Si series alloy, 6061 aluminium alloy has good mechanical processing performance and is widely used in aerospace construction and other industries [1]
The mechanical properties of material are determined by its microstructure
Some small defects appear during directional solidification, which results in the decline of mechanical properties of casting 6061 aluminium alloy with the increase of temperatures

Summary

Introduction

As Al-Mg-Si series alloy, 6061 aluminium alloy has good mechanical processing performance and is widely used in aerospace construction and other industries [1]. Processing parameters of directional solidification can be controlled to change microstructure and enhance the performance of 6061 aluminium alloy [2]. As early as the 1950s, Versnyder et al [3] developed a top-down temperature gradient using the heat-generating method. Since it is not possible to ensure the repeated production of high quality castings, Versnyder et al [4,5] proposed a directional solidification power reduction in the 1960s. High-speed solidification method is proposed by Erickson et al [5] in 1971. Giamei et al [6] invented a liquid metal cooling (LMC) method in 1976, which is relatively inexpensive and suitable for industrial production

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Conclusion