Solid-state welding offers distinct advantages for joining reactive materials, such as magnesium (Mg) and its alloys. This study investigates the effect of linear friction welding (LFW) on the microstructure and mechanical properties of cast AZ91 (Mg–9Al–1Zn) and AZ91–2Ca alloys, which (to the best knowledge of the authors) has not been reported in the literature. Using the same set of LFW process parameters, similar alloy joints—namely, AZ91/AZ91 and AZ91–2Ca/AZ91–2Ca—were manufactured and found to exhibit integral bonding at the interface without defects, such as porosity, inclusions, and/or cracking. Microstructural examination of the AZ91/AZ91 joint revealed dissolution of the Al-rich second phase in the weld zone, while the Mn containing phases remained and were refined. In the AZ91–2Ca/AZ91–2Ca joint, the weld zone retained Ca- and Mn-rich phases, which were also refined due to the LFW process. In both joint types, extensive recrystallization occurred during LFW, as evidenced by the refinement of the grains from ~1000 µm in the base materials to roughly 2–6 µm in the weld zone. These microstructural changes in the AZ91/AZ91 and AZ91–2Ca/AZ91–2Ca joints increased the hardness in the weld zone by 32%. The use of digital image correlation for strain mapping along the sample gage length during tensile testing revealed that the local strains were about 50% lower in the weld zone relative to the AZ91 and AZ91–2Ca base materials. This points to the higher strength of the weld zone in the AZ91/AZ91 and AZ91–2Ca/AZ91–2Ca joints due to the fine grain size, second phase refinement, and strong basal texture. Final fracture during tensile loading of both joints occurred in the base materials.

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In this work, a Mg-Sr-Ca alloy is evaluated for ignition resistance. The simultaneous use of Sr and Ca results in an ignition temperature increase of %110 C compared to pure Mg. This is attributed to the formation of a compact oxide scale due to the modification of the native MgO scale. A new parameter, the effective Pilling-Bedworth ratio (EPBR), which is the molar volume ratio between the oxide formed and the substrate alloy, is developed. The EPBR of the composite oxide forming on the Mg-Ca-Sr alloy is found to be greater than 1, resulting in a protective scale due to the increased volume occupied by the oxide at the surface. In the solid state, the oxide scale is rich in CaO, with the SrO contribution being minimal. In the liquid state, SrO contribution increases. MgO:CaO % 1:15 MgO:CaO % 1:1 MgO:CaO % 4:1 MgO:CaO % 2:1 CaO:MgO:SrO % 32:16:1 CaO:SrO % 10:1 EPBR % 0.84 EPBR % 0.97 EPBR % 1.05 EPBR % 1.01 EPBR % 1.03 EPBR % 1.16 670 C, 15 min M/O interface (1000 nm) Middle oxide (500 nm) G/O interface CaO:MgO:SrO % 4:40:3 CaO:MgO:SrO % 3:16:2 CaO:MgO:SrO % 5:1:9 EPBR % 0.85 EPBR % 0.89 EPBR % 1.33