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Pillari, Lava Kumar

University of British Columbia

The automotive industry is globally transitioning towards lighter vehicles to meet stringent fuel standards and reduce CO₂ emissions. The B319 aluminum (Al) alloy finds widespread use in automotive powertrain components due to its low density, good strength, and excellent castability. However, the poor tribological properties of the B319 Al alloy hinder its broader application in powertrain components. Graphene has been considered a promising reinforcement for Al matrices due to its ability to enhance multiple properties simultaneously while maintaining the lightweight characteristics of the alloy. However, graphene agglomeration and its poor wettability pose significant processing challenges, particularly in the casting process, thereby limiting the advancement of Al-graphene composites and their industrial adoption. Therefore, this study aims to fabricate B319 Al alloy-graphene (0-0.7 wt.%) composites utilizing a novel distribution approach. This approach involves the fabrication of composite master alloy (F357-5 wt.% graphene) through a flake powder metallurgy approach involving ball milling and spark plasma sintering. Subsequently, the composite master alloy was introduced into the B319 Al alloy melt to fabricate B319-graphene composites via stir casting. The effect of graphene on the microstructure, hardness, tribological behavior, electrical conductivity, and thermal conductivity of the B319 Al alloy was investigated. The results indicate that the addition of graphene decreased the grain size of the B319 Al alloy, primarily attributed to the additional nucleation sites provided by the presence of graphene. Moreover, adding graphene refined the Si phase and changed its morphology from a needle-like to a more fibrous structure. Consequently, the hardness of B319 Al alloy was enhanced by 20% with the addition of 0.1 wt.% graphene, but it deteriorated with graphene additions beyond 0.3 wt.%. Regardless of the load, the B319-0.3 wt.% graphene composite exhibited the best anti-friction and wear response compared to the base alloy. This improvement was attributed to the formation of a stable mechanically mixed layer (MML) or graphene-containing tribolayer at the contact surfaces. Wear in the base alloy primarily occurred via MML delamination through subsurface crack propagation, while wear in the B319-0.3 wt.% graphene composite was driven by MML fragmentation, accompanied by adhesive, oxidative, and abrasive wear mechanisms.

Text

2024-07-03

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/88556

Mechanical Engineering

University of British Columbia

UBCO

http://creativecommons.org/licenses/by-nc-nd/4.0/