Manufacturing aluminum/polybutylene terephthalate direct joints by using hot water–treated aluminum via injection molding

Metal–polymer direct joining helps meeting the growing demand for lightweight design in industry. Injection molded direct joining (IMDJ) is one of the promising metal–polymer direct joining methods. It needs firstly metal surface treatment and then injection insert molding. In this study, we proposed a simple, economical, and eco-friendly surface treatment, named as hot water treatment (HWT) for IMDJ. HWT produces complexed plate-like nanostructures on the aluminum surface. Polymer can flow into nanostructures and produce a mechanical interlocking effect by which metal and polymer achieve direct joining. The HWT treatment conditions, including water temperature and treatment time, were optimized. With the optimized condition, the highest joining strength of 22.5 MPa was obtained. An atomic force microscope (AFM) investigation on nanostructures and tensile shear tests to the joined specimens proved that the joining strength was strongly correlated with the combination of the arithmetical mean height (Sa) and the number of nanostructures (Nn). In addition, the joined specimens also achieved high cycle fatigue. Results showed that high-quality joint can be produced by treating aluminum with HWT. Compared with conventional chemical surface treatment methods, HWT is much easier to apply in practices. Wide applications in industries can be expected.