Microstructure and mechanical properties of complex-shaped 7075 aluminium alloy prepared using modified polyoxymethylene-based feedstock
(State Key Laboratory of Powder Metallurgy, Central South University, Changsha 410083, China)
Abstract: Additives of dioctyl phthalate (DOP), ethylene bis-stearomide (EBS), and epoxy (EP) were selected to modify the surface of 7075 Al alloy powder. Functional groups in DOP and EBS form hydrogen bonds with hydroxyl groups on the surface of Al powder. Additionally, the epoxy groups in the epoxy resin undergo ring-opening reactions with hydroxyl groups. The above interactions increased the compatibility between alloy powder and polyoxymethylene (POM). After sintering, samples containing DOP and EP presented high contents of C and O, while the part with EBS additive exhibited the lowest contents of 0.006 wt.% C and 0.604 wt.% O, respectively. Excessive C tends to accumulate at grain boundaries during sintering. Concurrently, excessive O causes secondary oxidation of aluminium alloy powder, inhibiting the sintering densification process. Therefore, the densities of the samples containing DOP and EP were only 85.52% and 79.01%, respectively. In contrast, using EBS as an additive, high-quality aluminium alloy parts were achieved, with a relative density of 97.64% and a tensile strength of 193 MPa.
Key words: 7075 aluminium alloy; polyoxymethylene-based feedstock; additives; compression moulding; metal injection moulding; microstructure; mechanical properties