Microstructure and Tribological Performance of Alumina–Aluminum Matrix Composites Manufactured by Enhanced Stir Casting Method

Abstract

Al–Zn–Mg–Cu matrix composites reinforced with (0–20 wt %) Al2O3 particles have been manufactured by enhanced stir casting technique. Microstructural characterization of cast composites by optical, field emission scanning electron microscope (FESEM), energy dispersive X-ray (EDS) and X-ray diffraction (XRD) reveals homogeneous distribution of reinforcements in Al-alloy matrix with MgZn2 plus Al2CuMg intermetallics. With increasing particle content, hardness of composite rises considerably in spite of marginal rise in porosity. Tribological performance under two-body abrasion has been studied considering central composite design (CCD) apart from identification of mechanisms of wear via characterizations of abraded surfaces and debris. Composites exhibit significantly reduced wear rate and coefficient of friction (COF) irrespective of test conditions, since mechanisms of abrasion are observed to change from microplowing and microcutting in unreinforced alloy to mainly delamination with limited microplowing in composites. Effects of four independent factors (reinforcement content, load, abrasive grit size, and sliding distance) on wear behavior have been evaluated using response surface-based analysis of variance (ANOVA) technique. Dominant factors on both wear rate and COF are identified as reinforcement content followed by grit size and load. Combined optimization of wear rate and COF employing multiresponse optimization technique with desirability approach as well as regression models of individual responses have been developed, and their adequacies are validated by confirmatory tests. The developed mathematical models provide further insight on the complex interactions among wear performances of the selected materials and variables of abrasive system. The optimum amount of reinforcement is identified at around 15 wt % for achieving the lowest values of both wear rate and COF.

Modelling of tribological responses of composites using integrated ANN-GA technique

“…Details of casting equipment, procedures and relevant processing variables were mentioned previously. 34 Based on spectroscopic method, composition of the prepared as-cast alloy specimen was evaluated to be Al-6.10Zn-2.51 Mg-1.93Cu conforming to the AA7075 alloy of ASM specification. Unreinforced matrix alloy, and composites comprising 5, 10 and 20 wt.% alumina reinforcements will hereafter be expressed in short forms as BA, 5CM, 10CM and 20CM respectively.…”

“…36 Firmly pasted emery papers (SiC grains) of varying grit sizes on a horizontally rotating steel disc were chosen as abrasive media. 34 Testing samples were made as cylindrical pins (6.3 mm (diameter) × 35 mm (height)). Test duration was multiplied by speed to generate line profiles of COF versus distance.…”

“…Subsequently, ANN based models for W rt , COF and RAS were developed considering generated experimental results and those reported elsewhere. 33–37 The developed ANNs models were employed as objective functions for multi-objective optimization through GA methodology. Finally, the criteria for designing improved DPAMCs as well as to indicate applicable tribo-conditions were emphasized and experimentally validated.…”

Identification and modelling of applicable wear conditions for stir cast Al-composite

“…In those trial tests, the distribution of particles in the metal matrix was considered as the sole criteria, and the same was assessed by microstructural characterizations and density measurements. For composite preparation, the constant stirring velocity of 500 rpm and stirring duration of 10 min were chosen [28]. Higher stirring speed caused greater entrapment of gases into the slurry, leading to higher porosity in the casting [29,30].…”

“…The particle distribution was found to improve with extending stirring time up to 10 min, beyond which there was no noticeable change observed from the microstructural investigation. The temperature of the Al-melt (i.e., bath temperature) during particle addition and subsequent stirring was fixed at 800 °C [28]. At lower bath temperature, particles could not be pulled deep into the melt even by the developed multistage stirrer due to higher viscosity of the melt.…”