Development and Machining of Aluminum Hybrid 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 study focuses on identification of most significant parameters for stir casting process, optimization of machining parameters for surface roughness, study of cutting tools and chips during machining process and corrosion study of newly developed composite material. Significant as well as non-significant factors have been identified from the literature survey and trial experiments. Without considering the significance of given responses, identified factors have been 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 unfavorable combination of parameters % porosity increased beyond 7% during screening design based experiments. Subsequently, these parameters have been optimized by factorial design. The result shows optimized parameters stirring speed 650 rpm and stirring time 12 minutes that 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 have been carried out to understand the effect of stirring, fluxing, degassing and molding 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. Different reinforcement amount was used to find their effect on strength to weight ratio, percentage porosity, wear rate and wettability. It was observed that porosity in AHMMCs reduces up to 2% with an increase in %wt of wetting agents. The strength to weight ratio increases with an increase in wt% of wetting agent and B4C. However, the wear rate reduces up to 57% with an increase in %wt of Mg and Graphite compared to pure aluminum. The wettability increases up to 40% with an increase in %wt of wetting agents. Thus, it is concluded that wetting agents play a significant role in the development of the specific properties of hybrid metal matrix composites (HMMCs). It was observed from the machining study that 2202 RPM spindle speed, 0.18 mm/rev feed rate and 1.1 mm depth of cut are the optimum turning parameters with PCD insert. While machining of same composites using carbide insert, optimum spindle speed, feed rate and depth of cut are 2091 RPM, 0.19 mm/rev and 1.1 mm respectively. Moreover, PCD insert provides better surface finish compared to carbide coated insert for same cutting conditions. Moreover, the effect of reinforcement particles presence on the surface finish was also investigated and it was concluded that reinforcement presence reduces the surface roughness considerably. Particularly presence of Mg and graphite reduces surface finish significantly. It was observed from the tool and chip study that the unfavorable machining parameter reduces tool life considerably. This phenomenon was more evident in the carbide coated insert compared to PCD insert. High tool wear was observed during machining of composite material compared to the aluminum matrix. An undesired chip produced when feed increases and speed reduces. However, change in reinforcement amount also has an effect on types of chip produces but that did not produce undesirable chips. The surface roughness value up to 0.50μm was reduced by a combination of optimized cutting parameters and change in reinforcement amount. It was observed from the corrosion study that initial corrosion rate of MMC happens to be higher compared to pure aluminum due to reinforcement but afterwards, it reduces due to the formation of the passive oxide layer and higher diffusion path length. Moreover, MMC with high carbon content (B4C and Graphite) shows the highest corrosion rate due to the presence of C. However, MMC with high Mg content shows better immunity against corrosion. MMC with high Ti initially shows higher corrosion rate due to the action of Ti-rich Al particles as anode but as time progresses a secondary protective oxide layer formation took place which reduced the corrosion rate. Keywords: Porosity, Wettability, Stirring, Screening, Optimization, AMMCs, UTS, Wear, Corrosion rate, Metal Matrix Composites, Simple Immersion, Pitting, Oxidation, Hybrid Metal Matrix Composite, Surface finish, Machining time, Reinforcement, Box- Behnken design, Tool wear, Chip analysis, Polycrystalline diamond, Surface roughness