Mechanical Behavior of As-Cast and Extruded Mg-Si-Ni-Ca Magnesium Alloys
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JMEPEG https://doi.org/10.1007/s11665-020-05229-3
Mechanical Behavior of As-Cast and Extruded Mg-Si-Ni-Ca Magnesium Alloys Omid Marjani, Massoud Emamy, and Hamed Mirzadeh Submitted: 12 September 2020 / Revised: 10 October 2020 / Accepted: 11 October 2020 The mechanical performance of as-cast and hot extruded Mg-4Si-4Ni-xCa alloys was studied. In the as-cast microstructures, the dendritic primary Mg2Si particles, eutectic a-Mg + Mg2Si constituent, blocky v-phase (Mg8Ni7Si5 intermetallic), and a-Mg phase were observed. Moreover, the needle-shaped CaMgSi intermetallic at high Ca additions was detected. The modification effect of Ca was discussed based on the size refinement and morphological enhancement of Mg2Si phase. Accordingly, the tensile properties of the ascast alloys were enhanced by Ca addition no more than 1 wt.%. However, large additions (3 wt.%) resulted in the deterioration of strength and ductility due to the appearance of the needle-shaped CaMgSi intermetallic. Compared to the cast ingots, the wrought alloys (obtained by hot extrusion) showed superior mechanical performance with much larger work-hardening exponents and tensile toughness values. For instance, the tensile toughness of the extruded alloy with 1 wt.% Ca was determined as 78.65 MJ/m3, which is much higher than the value of 9.32 MJ/m3 for the as-cast 0 wt.% Ca alloy. As the best combination of tensile properties, the ultimate tensile strength and the total elongation of the extruded alloy with 1 wt.% Ca were 348.4 MPa and 16.6%, respectively. Keywords
hot deformation, hybrid intermetallics, magnesium properties, modification
in situ alloys,
composite, mechanical
1. Introduction Magnesium alloys are used extensively in aerospace, chemical, medical, and automotive industries due to low density and desirable attributes such as damping, machinability, and castability (Ref 1-6). However, insufficient strength and poor ductility limit their applicability. Alloying (Ref 7-11), grain refinement (Ref 12-16), hot working (Ref 17-21), and adding reinforcement particles (composite strengthening) (Ref 22-25) are among the viable methods for improvement of mechanical performance of Mg alloys. In the case of composite strengthening, the in situ formation of particles has attracted considerable attentions, which can be ascribed to the costeffectiveness of this process as well as the observed good particle-matrix interface and uniform distribution (Ref 26-28). Due to the simplicity of the processing of Mg-Mg2Si composites by the addition of Si to Mg, the Mg2Si intermetallic is an attractive in situ formed phase (29-31). However, the MgSi alloys usually show low strength and ductility due to the presence of the large Mg2Si particles with the dendritic morphology and the brittle eutectic constituent (Ref 31). Therefore, modification in the Mg-Si and Al-Mg-Si alloys via micro-addition of a modifying element has been practiced (32-
Omid Marjani, Massoud Emamy, and Hamed Mirzadeh, School of Metallurgy and Materials Engineering, College of Engineering, University of
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