Abstract

This study examines the impacts of key abrasive water jet machining (AWJM) parameters on the machinability of AA7175–15 wt.% ZrB2 metal matrix composites produced via a two-step stir casting route. Jet pressure (100–300 MPa), traverse speed (70–130 mm/min), standoff distance (3–5 mm), and abrasive flow rate (250–450 g/min) were systematically varied to evaluate their effects on surface roughness (Ra), kerf taper angle (KA), and material removal rate (MRR). The experimental setup was designed using response surface methodology based on a central composite design (RSM–CCD), enabling both interaction and curvature effects to be assessed. Analysis of variance indicates that jet pressure exerts the strongest influence on MRR, which may be attributed to the increased kinetic energy and penetration capability of abrasive particles at higher pressures. In contrast, traverse speed was found to play a dominant role in controlling surface roughness and kerf geometry. As traverse speed increased, Ra and kerf taper angle tended to rise, likely due to reduced jet–material interaction time and incomplete erosion of the hard ZrB2-reinforced matrix. Abrasive flow rate contributed positively to MRR up to higher levels, although its effect appeared secondary compared to jet pressure. Regression models developed for all machining responses showed strong predictive performance, with coefficients of determination exceeding 0.95 and statistically insignificant lack-of-fit, suggesting adequate representation of the underlying process behaviour within the investigated parameter range. Scanning electron microscopy of the machined surfaces revealed erosion features such as abrasive ploughing, particle pull-out, and striation formation. These surface morphologies are consistent with the observed variations in Ra and kerf characteristics and reflect the combined ductile–brittle erosion response of the composite. Overall, the study identifies optimised AWJM parameter combinations that can improve both surface quality and machining efficiency when processing AA7175–ZrB2 composites.

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