عنوان مقاله [English]
Two alloys of Al-Zn-Mg-Cu with the same amount of zirconium and different amount of scandium (0.05 and 0.1 wt.%) were melt in the resistance furnace and cast in the cast iron mold and, after doing the tests of ICP, Spectroscopy and DSC, were put under homogenizing, solubility and T6 treatments operations. Using microscopic observations and DSC analysis, the temperature and time of homogenizing the alloys samples were 500°C and 12h and, 490°C and 12h for Al-Zn-Mg-Cu-0.1Sc-0.09Zr and Al-Zn-Mg-Cu-0.0.05Sc-0.09Zr, respectively. At the dissolution temperature obtained from the results of hardness test and microscopic observations by FESEM, the alloys were subjected to dissolution and then, were put under T6 thermal operations at 120°C for 12 hours. Microscopic investigations showed that the dominant phases in the microstructure of casting were along with T (Al2Mg3Zn3 and copper solid solution and MgZn2 phase, and the eutectic phase formed 10% of the microstructure. Also, investigation of the casting and homogenized microstructure revealed that no phase included scandium and zirconium in the microstructure. After the homogenization operation, the eutectic phase decreased to 3%. The dominant phase observed in the homogeneous microstructure was the phases containing iron. After the dissolution, the volume fraction of the eutectic phase remained constant and the MgZn2 phase. Having performed the T6 thermal operation at 120°C, Al3(Sc,Zr) and MgZn2 nanoparticles were observed at the grain boundary and inside the microstructure.
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