Research on interfacial microstructure, mechanical properties, and damage behaviors of AZ91/GWZ831K bimetallic structures fabricated via wire-arc directed energy deposition

Abstract

This study investigated the interfacial microstructure, mechanical properties, and tensile damage evolution behavior of AZ91/GWZ831K bimetallic structures fabricated by wire-arc directed energy deposition (WA-DED). Bimetallic specimens were prepared with two distinct deposition sequences, and significant differences in interfacial morphology, elemental distribution, and precipitation characteristics were observed between the two groups. Specifically, the AZ91-GWZ831K (AG) bimetallic sample, with AZ91 deposited first, formed a wavy mechanical interlocking interface, where brittle Al 2 Gd phases were confined within a narrow region of approximately 8 µm. In contrast, the reversely deposited GWZ831K-AZ91 (GA) sample exhibited a transition zone with a thickness of 2.5 mm above the interface, which was enriched with continuous bead-like Al 2 Gd precipitates. This layer exhibited lower microhardness, indicating a mechanically weak zone. The AG sample demonstrated a superior ultimate tensile strength (UTS) of 253.2 MPa and elongation (EL) of 12.81% compared with the GA sample (UTS: 235 MPa, EL: 9.26%). In-situ X-ray computed tomography (XCT) revealed that the mechanical interlocking structure of the AG sample effectively inhibited crack propagation. For the GA sample, continuously distributed brittle intermetallic compounds (IMCs) promoted crack initiation and accelerated subsequent propagation along the soft transition layer.