In situ self-generation and joint strengthening mechanisms of low melting point layered Mg-Zn filler

• A filler was designed and prepared to achieve the high strength joining of Mg alloy brazed joints at low temperatures. • The α'-Mg/Mg 7 Zn 3 (MgZn 2 ) soft-hard biphasic heterogeneous structure formed during brazing solidification enhances shear strength enhances shear strength. • The low-temperature joining of Mg alloys was achieved through local melting of the low melting point Mg 7 Zn 3 phase inducing the overall gradient melting. Brazing of magnesium (Mg) alloys is critical for lightweight structural application, but the inherent brittleness of intermetallic compounds (IMCs) formed in conventional Mg alloy fillers severely limits joint reliability and precision. In this work, a novel in situ self-generating Mg-Zn filler was developed through rolling compounding and diffusion reactions to enable low-temperature precision brazing. The filler significantly enhances joint performance, achieving a maximum shear strength of 54.6 MPa. This exceptional strength originates from the formation of an α′-Mg/Mg 7 Zn 3 (MgZn 2 ) soft-hard biphasic heterostructure during brazing solidification. The ductile α′-Mg phase effectively blunts crack tips, suppresses crack propagation, and relieves stress concentration in the hard-brittle Mg 7 Zn 3 (MgZn 2 ) phases, improving overall toughness and reliability. Meanwhile, rapid Zn diffusion during brazing induces atomic size mismatch within the α-Mg matrix, generating lattice distortion and dislocation proliferation. These structural defects lower the nucleation barrier of IMCs and promote the formation and localized melting of Mg 7 Zn 3 , which triggers gradient melting of the filler and enables effective low-temperature joining. This work provides a new filler design strategy and theoretical insights for advancing precision brazing of lightweight Mg alloys.