Microstructure and mechanical properties of friction stir welded AA6092/SiC metal matrix composite

Omar S Salih,Hengan Ou,Xingguo Wei,W Sun

doi:10.1016/j.msea.2018.10.116

Omar S Salih, Hengan Ou + Show 2 more

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https://doi.org/10.1016/j.msea.2018.10.116

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Abstract

There is a need for improved understanding on the effects of friction stir welding (FSW) on the metallurgical and mechanical properties of aluminium matrix composite (AMC). In this study, AA6092/SiC/17.5p-T6 AMC joints were produced by using FSW with varying tool rotation and traverse speeds. The microstructural characterisation by scanning electron microscopy equipped with electron backscattered diffraction (EBSD) system revealed a substantial grain refinement and a homogeneous distribution of reinforcement particles in the nugget zone. The grain size of the nugget zone was greatly influenced by weld pitch, as a key indicator to control the amount of heat input, exposure time and cooling rate. Vickers microhardness proﬁle across the welding zone revealed a signiﬁcant difference in microhardness among the base metal, heat affected zone, thermo-mechanically affected zone and nugget zone. The tensile strength of the cross-weld specimens showed a high joint efficiency of about 75% of the base metal combined with relatively high ductility. Low-cycle fatigue properties were investigated in the axial total strain-amplitude control mode (from 0.3% to 0.5%) with R=εmin/εmax=−1. The results indicate that the fatigue life of the cross-welded joints varies with grain size in the nugget zone and it is lower than that of the base metal. A significant improvement of fatigue life is found to be related to the finer equiaxed grains dominated by high angle grain boundaries in the nugget zone.

Highlights

Advanced materials like aluminium matrix composite (AMC) are considered to have considerable potential for lightweight applications due to their superior mechanical and physical properties at elevated and ambient temperature, compared to the unreinforced aluminium alloys [1]
Welding temperature and thermal history confirmed experimentally by Sato et al [27]. This observation can be related to the reduction of the friction coefficient and torque when the weld metal softens at a high temperature, which leads to a reduction in heat generation by mechanical work and stabilises the temperature to avoid the melting of metal [28]
It is evident that the temperature gradient from the peak temperature of the nugget zone (NZ) decreases with the reduction of traverse speed

Summary

Introduction

Advanced materials like aluminium matrix composite (AMC) are considered to have considerable potential for lightweight applications due to their superior mechanical and physical properties at elevated and ambient temperature, compared to the unreinforced aluminium alloys [1]. Regarding the joining of AMC by the conventional welding process, it has been observed that there is a deleterious reaction between the molten metal and reinforcement particles with inhomogeneous redistribution of reinforcement particles frequently occurred in the fusion zone [6]. The weldability of AMC by fusion processes is limited, and the attractive mechanical properties of these materials have yet to be entirely utilised [7,8]. FSW of AMC is not an easy task, and significant challenges remain in achieving optimum welding window and sufficient mechanical properties [11]

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