Effect of anhydrous borax addition and manufacturing method on aluminium-based in-situ formed metal matrix composites

This study aims to fabricate cost-effective aluminium matrix composites reinforced with in situ formed aluminium diboride (AlB₂) by incorporating 5 vol% micronised anhydrous borax (AHB) into the ETİAL 150 (EA150) aluminium alloy. Two manufacturing methods were compared: melting AHB and EA150 together in a single crucible (Method 1) and melting them separately before mixing them in a single crucible (Method 2). The influence of these methods on the physical, mechanical, and tribological properties of the composites was evaluated. Non-pressure casting was performed at 1000°C with rapid water-bath cooling to promote AlB₂ formation and suppress the brittle AlB₁₂ phase. Characterisation included density, Brinell hardness, pin-on-disc wear, three-point bending, and microstructural analysis. The results show that Method 2 effectively reduced slag and inclusions, improved Brinell hardness (up to 16.33%) and flexural yield stress (up to 11.10%), and a reduced coefficient of friction (by 5%) compared to pure EA150. These findings demonstrate that the manufacturing method critically controls the composite quality and performance, validating untreated micronised borax as a cost-effective boron source for AlB₂-reinforced aluminium composites suitable for structural and automotive applications.