Structural and mechanical properties of Al-25Zn-Ti alloys Effect of titanium on the microstructure, mechanical and corrosion properties of Al-25Zn-Ti alloy Grain refinement with titanium Figure A. The variations in hardness, yield strength, tensile strength, elongation to fracture of Al-25Zn-(0.01-1)Ti alloys with titanium content.
Purpose:The main aim of this study is to investigate grain refinement effect of titanium on the microstructural, mechanical and corrosion properties of new alloys produced by adding different ratios of titanium to the Al-25Zn based alloys.
Theory and Methods:In this study, one binary Al-25Zn and eleven ternary Al-25Zn-Ti alloys were produced by permanent mold casting method. Microstructures of the produced alloys were examined with standard metallographic techniques including SEM examinations and XRD studies. Grain sizes of the alloys were measured by the linear intersection method. Hardness values of the alloys were measured by using Brinell test method. The values of yield strength, tensile strength, and elongation to fracture of the alloys determined with tensile test. Corrosion tests were carried out according to ASTM G5 standard with electrochemical experimental setup.
Results:Titanium additions significantly reduce grain size of the Al-25Zn alloys. Al3Ti phase begins to form in the microstructure of the Al-25Zn alloy after 0.01% titanium content. The values of hardness, yield strength, tensile strength, and elongation to fracture of the Al-25Zn-Ti alloys increase up to 0.01%Ti content, but above it these values decrease
Conclusion:Titanium can be used in the Al-25Zn alloys as a grain refiner. Certain rates titanium addition positively affects the hardness, strength, elongation to fracture, and quality index of the Al-Zn alloys. However, addition of it to Al-25Zn alloys deteriorates corrosion resistance.
In order to determine the effect of working conditions on the lubricated wear behavior of Zn-40Al-2Cu-2Si alloy in the as cast and T6 heat-treated states, its tribological properties were studied at different oil flow rates, contact pressures, and sliding speeds in comparison with SAE 660 bronze. It was observed that the friction coefficient, temperature, and wear volume of both materials decrease, but their average surface roughness increase with increasing oil flow rate. As the pressure increased, the friction coefficient and average surface roughness of the experimental materials decreased, but their temperature and wear volume increased. It was also found that the working temperature of these materials increased, but their wear volume showed a decrement and a subsequent increment with increasing sliding speed. In addition, their wear volume and average surface roughness showed opposite changes with the sliding speed. The results of the lubricated friction and wear tests were discussed in terms of the microstructure and mechanical properties of the experimental materials and test conditions. Zn-40Al-2Cu-2Si alloy in both as cast and heat-treated conditions showed lower wear volume and friction coefficient than SAE 660 bronze. This indicates that Zn-40Al-2Cu-2Si alloy can be used to manufacture diesel engine crankshaft journal bearings.
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