Effects of zinc concentration on the stretch formability of the rolled Mg Zn Ca alloys were investigated. The zinc addition more than 0.5 mass effectively modified the basal plane texture, which was characterized by the splitting basal pole toward the TD. The intensity of basal plane texture decreased with the increase in zinc concentration. The rolled Mg 1.5 massZn 0.1 massCa alloy showed significant stretch formability corresponding to the rolled aluminum alloys. On the other hand, the zinc addition more than 1.5 mass deteriorated the stretch formability of rolled Mg Zn Ca alloys. The deterioration of the stretch formability of rolled Mg Zn Ca alloys with high zinc concentration was suggested to be responsible for the solid solution hardening. It was suggested that not only the TD split texture but also the solid solution softening played an important role in the enhanced stretch formability of the rolled Mg Zn Ca alloys.
Effects of Al concentration and Zn addition on microstructures and mechanical properties of Mg-Al-(Zn)-Ca series magnesium (Mg) alloy medium plates were investigated. Concerning to mechanical properties of AMX (Mg-Al-Ca) alloys with various Al concentrations, which were processed by rolling at 523 K and final annealing at 473 K, good balance of tensile strength and failure elongation were obtained, when Al concentration was 8 mass%. When Al concentration was more than 9 mass%, however, both tensile strength and failure elongation were deteriorated due to coarsening of Al-Ca compounds. Concerning to mechanical properties of AZX (Mg-Al-Zn-Ca) alloys with various Al concentrations and 1 mass% Zn addition, which were processed by the same procedure with AMX alloys, enhancement of tensile strength without deterioration of failure elongation was attained at Al concentration of 6-8 mass%, when the tensile direction was parallel to the rolling direction. Clear deterioration in failure elongation compared with AMX alloys were observed, however, when the tensile direction was perpendicular to the rolling direction. 1 mass%Zn addition to AMX alloy promoted precipitation of fine Mg 17 Al 12 particles, which likely affected mechanical properties. In addition, solid solution of Zn in AMX alloy likely contributed to enhancement of tensile strength.
Stress corrosion cracking (SCC) and corrosion resistance of Mg-6 mass%Al-1 mass%Zn-1 mass%Ca (AZX612) extruded alloy were investigated by slow strain rate tensile tests (SSRT) in 0.01 M NaCl solution and immersion tests in 5 mass% NaCl solution, and compared with those of Mg-6 mass%-1 mass%Zn (AZ61) extruded alloy. In the SSRT in the salt solution, as-received AZX612 exhibited lower elongation and higher SCC susceptibility than those of as-received AZ61, indicating that calcium addition in Mg-Al alloy deteriorated SCC resistance. On the other hand, after solution treatment, improvement of elongation and SCC susceptibility occurred in both the alloys. Observation of surface profiles for AZX612 and AZ61 after the SSRT in salt solution revealed that corrosion pits on surface likely initiated SCC in both the alloys. The results of immersion tests showed the same tendency with those of SSRT in salt solution. It is suggested that SCC resistance of AZX612 and AZ61 was likely related to the microstructural change accompanied with calcium addition and solution treatment such as the change in distributions of Al 2 Ca phase and Al-rich phase.
The effects of Al concentration and Zn addition on the corrosion resistance of Mg-Al-(Zn)-Ca based magnesium (Mg) alloy rolled sheets were investigated. AXM (Mg-Al-Ca) alloys containing 1 mass%Ca, and AZX (Mg-Al-Zn-Ca) alloys containing 1 mass% of Ca plus 1 mass%Zn, both adjusted the Al concentration to 6, 7, 8, 9, 11 mass%, were prepared. The corrosion resistance of alloys in 5 mass%NaCl solution was evaluated by the weight loss and the penetration depth. Electrochemical method based on corrosion potential and impedance spectroscopy was applied to monitor the corrosion behavior. The surface film formed on the alloy surface was characterized by GD-OES and SEM/EDS. The corrosion rates were minimal for AXM alloy with Al content of around 8 mass%Al whereas AZX alloy showed the opposite result with the same content. The reason was interpreted in terms of the Al concentration in the matrix (α phase). The tendency of localized corrosion in high Al-containing Mg alloys was pointed out.
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