Abstract
This paper illustrates the effects of stirring and graphene nanosheet (GNS) addition on the microstructure and mechanical behaviour of 393 hypereutectic Al-Si alloys used in the diesel engine pistons. Two processing routes were applied to fabricate hypereutectic Al-Si alloys: The first route mainly depends on stirring Al-Si alloys for 12 minutes at 400 rpm. The second one involves stirring Al-Si alloys for 2 minutes and then adding graphene nanosheets into the vortex, and consequently continue stirring for 10 minutes at 400 rpm. Results show that the distribution of the primary silicon was improved significantly in stir casting at both the edge and the center of the samples with relative reduction of 34% and 37% in the average particle size respectively. This average primary silicon size was further reduced by 17% with the addition of 1 wt% GNSs. GNS embedding into Al-Si alloy matrix resulted in remarkable increase in hardness values of the nanocomposites compared to the cast alloy.
Highlights
The number of researches on the Al-Si alloys used in automotive industries has increased due to the demand of improving wear resistance and fatigue strength [1]
Pure silicon crystals structure in both primary and eutectic are the form that present in hypereutectic aluminum-silicon alloys
Silicon particle crystals are harder than any other phases, which can typically be found in aluminum casting alloys
Summary
The number of researches on the Al-Si alloys used in automotive industries has increased due to the demand of improving wear resistance and fatigue strength [1]. Hypereutectic Al-Si alloys usually contain coarse primary silicon particles (PSPs), eutectic silicon and eutectic alpha phases. Authors in [8] reported that specific casting techniques such as spray and centrifugal casting can refine the microstructure of the hypereutectic Al-Si alloys and uniform Si distribution. This refined microstructure and uniformed distribution can lead to improved strength, ductility and hardness
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