RESUMO
To further improve the mechanical properties and corrosion resistance of the biodegradable magnesium (Mg) alloy, the Mg-4Zn-0.5Sr-xAg alloy (x = 0.2 wt.%, 0.5 wt.%, 1.0 wt.%, and 2.0 wt.%) was smelted in vacuum under the protection of inert gas. The effect of the Ag content on the microstructure and mechanical properties of Mg-4Zn-0.5Sr was tested. The results show that the comprehensive properties of Mg-4Zn-0.5Sr-0.5Ag are best. The grain size of the Mg-4Zn-0.5Sr-0.5Ag alloy is minimal, that is, 83.28 µm. The average tensile strength (σb), yield strength (σs), elongation (ε), and hardness for the Mg-4Zn-0.5Sr-0.5Ag alloy is 168.00 MPa, 88.00 MPa, 12.20%, and 59.90 HV, respectively. To further improve the properties of cast Mg-4Zn-0.5Sr-0.5Ag alloy, extruding treatment was conducted. After extrusion deformation, the grain size of the alloy was significantly refined to 9 µm; at the same time, fine second phases were formed and evenly distributed in the matrix. And then, the mechanical properties of the alloy are significantly enhanced due to the effect of fine crystal strengthening and dispersion strengthening. The σb, σs, ε, and hardness value for the extruded Mg-4Zn-0.5Sr-0.5Ag alloy are 236.00 MPa, 212.00 MPa, 18.97%, and 65.42 HV, respectively. Under the synergistic action of adding the Ag element and extrusion treatment, the grain size of the alloy was significantly refined and the coarse second phase in the alloy became refined to disperse in the matrix, which benefits the formation of electric couples characterized as small cathode-large anode between the second phase and Mg matrix. During full immersion, corrosion products covered on the large anode surface could reduce the galvanic corrosion tendency.
RESUMO
The current protocol presents the effects of the addition of Cu, rare earth Er, and Cu-Er composite elements on the microstructure of the Al-10Si-0.3Mg alloy. The variations in their low-temperature tensile properties were also investigated. The addition of rare earth Er elements, Cu elements, and Cu-Er composite elements increased the strength of all three groups of alloys when stretched at low temperatures (-60 °C). Further, the elongation of the alloy increased with the addition of Er, while the elongation of the other two groups decreased. The low-temperature (-60 °C) tensile strength of the alloy with the same composition was higher than that at room temperature (20 °C), but the elongation decreased. Notably, by adding rare earth Er to the Al-10Si-0.3Mg alloy, the three-dimensional morphology was changed from coarse dendritic to fine fibrous, the secondary dendritic arm spacing (SDAS) of the alloy was reduced, and the grains were refined. The Al2Cu phase, Al-Si-Cu-Mg quaternary phase, and Cu-rich phase appeared in the alloy with the addition of Cu elements, but the Si phase morphology and α-Al dendrites were not significantly improved. Interestingly, the Si phase morphology of the alloy was improved by adding Cu-Er composite elements, and SDAS was reduced. Still, the Al2Cu phase, Al-Si-Cu-Mg quaternary phase, and Cu-rich phase were not much improved.
RESUMO
In order to investigate the effect of Mg2Si formation on the microstructure and properties of an Al-Si alloy, the critical point of a hypereutectic Al-17Si-4Cu-Mg alloy was calculated by Pandat software. The calculation results of the equilibrium phase diagram show that the critical point for Mg2Si phase formation for the alloy was obtained when the Mg content was 2.2%. The contents of 0.5 wt.% Mg and 2.5 wt.% Mg were selected as the research object. The content of Mg increased from 0.5 wt.% to 2.5 wt.%, the eutectic Si in the matrix was reduced, and the Chinese character-like Mg2Si phase appeared in the microstructure. In the peak ageing state, in addition to θⳠand Q' phases that were mainly precipitated, there was also needle-like ßâ³ precipitation in the 2.5 wt.% Mg content alloy. Larger precipitates were found in 2.5 wt.% content alloys, mainly due to the promotion of the solid solution having the aggregation and segregation of more solute elements in the matrix. The tensile strength, elongation, and hardness of hypereutectic Al-17Si-4Cu-0.5Mg alloy under peak ageing were 331 MPa, 3.11%, and 152.1 HB, respectively. The tensile strength and the elongation decreased while the hardness increased with the 2.5 wt.% Mg content, which is due to the formation of hard and brittle Mg2Si and Al8FeMg3Si, which has a splitting effect on the matrix.
