Roll Bonding of Aluminium Coupons Using the Established Fully Fledged Offline Fabrication Facilities

The South African aluminium industry faces technical challenges related to cladded ingots used in automotive heat exchangers, creating a need for offline processing methods that can replicate rolling processes like roll bonding, as large-scale industrial trials are costly and difficult to control. To address this, Mintek established a comprehensive offline manufacturing facility for process and product development of rolled metal products, focusing on the thermomechanical processing of aluminium alloys. In this study, stacked AA4045/AA3003mod coupons were processed under controlled conditions by varying thickness reduction, temperature, and reheating, aiming to investigate the effect of isothermal soaking time on microstructure and mechanical properties. Tensile tests were performed on clad sheets before and after brazing heat treatment, and fracture surfaces were examined via scanning electron microscopy. Samples heated at 505 °C for ≥38 h, followed by cold rolling and annealing, fell at the lower end of the 9031-H24 specification for yield strength, which is important for this application (i.e., the minimum tensile yield strength of 145 MPa and the ultimate tensile strength (UTS) range of 190 to 230 MPa). Fracture surface analysis revealed a dimple-dominated structure in cold-rolled and annealed samples, indicating ductile fracture. The study concludes that the offline roll-bonding method successfully replicates industrial cladding processes, and that isothermal soaking duration significantly influences mechanical performance, though careful control of thermal exposure is necessary to meet the specified mechanical properties.