Recovery of AA7075 alloy and TiC-rich powder from laboratory-generated unusable AA7075/12 wt.% TiC composite using Box–Behnken design

Abstract

This study investigates the recovery of AA7075 alloy and pre-existing in situ-formed TiC reinforcement from laboratory-generated, unusable AA7075/12 wt.%TiC metal matrix composite scrap. Controlled remelting experiments were designed using 17-run Box–Behnken design, and the effects of holding time, melting temperature, and sprue height on AA7075 recovery were evaluated using Response Surface Methodology and analysis of variance. The 17-run BBD and a separate 1700.00 g bulk material-accounting experiment are reported independently. In the bulk experiment, the calculated nominal TiC content was 204.00 g (12 wt.% of the feed basis), and 1125.00 g of AA7075 was collected, corresponding to 75.23% matrix recovery. The highest measured BBD recovery was 75% at 30 min, 750°C, 10 mm and at 45 min, 700 °C, 10 mm. Sprue height was the most influential factor (F = 921.35, p < 0.0001), although its effect reflects melt transfer and collection geometry as well as separation. Two selected residue samples (104.30 and 103.00 g) were treated with 2 M HCl, yielding 204.00 g of dried TiC-rich powder. Because residue input was weighed before drying and carbon was estimated by difference, no TiC recovery efficiency or purity-corrected yield is claimed. SEM, XRD and XRF provided morphological, qualitative phase and compositional evidence, respectively.