Identification, screening and optimization of significant parameters for stir cast hybrid aluminium metal matrix composite

Abstract

Different industries have explicit applications of Aluminum Metal Matrix Composites (AMMCs). However, porosity, wettability and Ultimate Tensile Strength (UTS) are important factors that need to consider while fabricating AMMCs. This paper focuses on identification of the most significant parameters for low porosity and high ultimate tensile strength (UTS) of hybrid aluminium metal matrix composite. Significant as well as non-significant factors were identified from the literature survey and trial experiments. Without considering the significance of given responses, identified factors were represented graphically by the fishbone diagram. FMEA (Failure Mode and Effect Analysis) was used to find out significant parameters from all the parameters that represented by fishbone diagram. Afterwards, Plackett-Burman design was used to screen the most significant parameters out of the significant parameters. Stirring speed, stirring time, preheating temperature and reinforcement amount was found the most significant parameters to attain high UTS and low porosity. However, because of the unfavourable combination of parameters % porosity increased beyond 7% during screening design based experiments. Subsequently, these parameters were optimized by factorial design. The result shows optimized parameters stirring speed 650 rpm and stirring time 12 minutes provides low porosity and high UTS. UTS improved up to 310 MPa due to an optimized range of stirring speeds and stirring time. However, porosity increased beyond 3% due to excess stirring in cast composites during factorial design based experiments. Moreover, studies were carried out to understand the effect of stirring, fluxing, degassing and moulding methods on porosity, UTS, clustering and surface finish of the cast composite. It was observed from a supplementary study that permanent mould reduces surface roughness below 3μm, compared to the sand casting process. The porosity was reduced below 3% by degassing and fluxing. Low agglomeration was observed in specimen prepared with automatic stirring process compared to the manually stirred specimen. Compared to others, in specimen 4, UTS was improved beyond 150 MPa because of permanent mould, automatic stirring, degassing and fluxing.