Heat treatment induced strength improvement of the injection-molded joint between polymer and blasted steel

Abstract

Blasting treatment faces the problem of insufficient joining strength when it is applied to metal-polymer direct joining via injection molding. In this study, a secondary heat treatment was proposed to improve the joining strength of abrasive-blasted steel and polymer joints. After the heat treatment, flower-like nanostructures were produced on the steel surface and the surface roughness Sa increased from 112.9 nm to 145.0 nm, providing more space for molten polymer to flow into. The surface free energy of steel surface increased to 76.2 mN/m after the heat treatment, indicating the improvement of steel surface wettability and less resistance for polymer infiltration. The joining strength increased by 45 % and reached 24.5 MPa via the heat treatment. Through fracture surface observation, the occurrence of cohesive failure further confirmed that the heat treatment effectively improved the mechanical interlocking at the joining interface.