Valorizing Coal Fly Ash in Graphene-Reinforced Aluminum Hybrid Composites: Taguchi Optimization of Powder Metallurgy Parameters

Abstract

This study screens four powder-metallurgy variables for reported aluminum/carbon-reinforcement/fly-ash composites (5–15 wt% total reinforcement) using a Taguchi L9 array. Hardness (three indents per condition) varied from 48.13 to 50.07 VHN; Archimedes bulk density varied from 2.493 to 2.560 g/cm³. Main-effect allocations ranked milling time (56.55%) and reinforcement fraction (32.56%) highest for hardness, but holding time (38.24%) and sintering temperature (32.62%) highest for density. These are descriptive screening contributions because the L9 design is saturated. The hardness model predicts approximately 50.37 VHN at 15 wt% reinforcement, 2 h milling, 550 °C and 0.5 h holding. A reported ≈4.4% confirmation gain lacks raw replicate data and uncertainty; its implied value also requires reconciliation with the model prediction. The narrow property ranges and absence of independent batch replication preclude claims of engineering benefit or statistical significance. The original Figure 1 labels the carbon material graphene oxide, whereas the text states graphene nanoplatelets; its chemical identity needs verification. Relative to existing graphene-only, fly-ash-only and other-hybrid studies, the contribution is a material-specific, dual-response process screening rather than demonstrated superiority or a new optimization method.