Abstract
In this work, a fine-grained structure with a uniform distribution of TiB2 particles and precipitates was achieved in TiB2 particle-reinforced (PR) Al-Zn-Mg-Cu alloys by friction stir processing (FSP). The effects of multi-pass FSP on the microstructure, and TiB2 particle distribution, as well as the microstructural evolution in the following T6 treatment, were investigated by X-ray diffraction, scanning electron microscopy and associated electron backscattered diffraction. The results showed that the distribution of TiB2 particles and alloy precipitates was further improved with an increase in the FSP passes. Moreover, compared with alloy segregation in the as-cast PR alloys during T6 treatment, a complete solution of the precipitates was achieved in the FSP-treated PR alloys. The fine-grained structure of the FSP-treated PR alloys was thermally stable without any abnormal growth at the high temperature of T6 treatment due to the pinning effect of dispersed TiB2 particles. The strength and ductility of the PR alloys were simultaneously improved by the combination of FSP and T6 treatment.
Highlights
In the past decades, in order to improve the mechanical properties of aluminum alloys, nano-sized ceramic particles such as TiB2, SiCp [1] and TiC [2] have been introduced to alloy matrixes as reinforcements to fabricate nano-particulate-reinforced alloy matrix composites
The typical microstructure of the network-like areas are the clusters of TiB2 particles on the micrometer scale with alloy segregation the as-cast PR alloy shows equiaxed grains with an average grain size of about 27 μm, embedded rich in Mg, Zn and Cu elements
The best friction stir processing (FSP) condition is four-pass, where the yield strength (YS) is increased by 48% and the ultimate tensile strength (UTS) by 30% compared with
Summary
In order to improve the mechanical properties of aluminum alloys, nano-sized ceramic particles such as TiB2 , SiCp [1] and TiC [2] have been introduced to alloy matrixes as reinforcements to fabricate nano-particulate-reinforced alloy matrix composites. By reducing the reinforcement particle size to the nanometer range, it has been reported that the tensile ductility of such PR alloys can be maintained or even enhanced with a simultaneous increase in tensile strength, depending on the processing process [3,4,5]. Casting (i.e., liquid-state solidification) generally weakens ductility and toughness due to defects like porosity, particle-matrix debonding, and especially particle clustering [6]. It is very tough work to distribute nanoparticles uniformly in the metal matrix [7]. Previous studies show that the particle clusters further have a negative effect on the solution treatment. Hong et al [10] studied TiB2 /2009 composites and found that the presence of nanoparticle clusters
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