The optimum Ni content in the modified 5052 alloy by electron beam alloying was investigated based on the measurement of the mechanical strength of the modified 5052 alloys and the strength of the interface between the substrate and the modified alloys. The X-ray diffraction or EDX analysis of the precipitates, the scanning electron microscopic observations of the samples with or without modification and the fracture surfaces after tensile tests were also performed.
The main results obtained are summarized as follows:
(1) Three types of structures were observed in the modified 5052 alloys: fine Al(α) grain, Al(α)+Al3Ni(β), and coarse Al3Ni(β) intermetallic particles. The surface area ratio of the Al+Al3Ni(β) eutectic structure increases with increasing Ni contents below 8 mass%, whereas the ratio decreases at Ni contents higher than 8 mass%. Furthermore, the surface area ratio of the large size Al3Ni intermetallic compound increases with increasing Ni content. (2) The Vickers hardness of the modified alloys increases with increasing Ni content in the alloy. The mechanical strength such as the U.T.S. of the modified alloys increases with increasing Ni content below 5 mass% and the values of 300 MPa is almost constant at Ni contents from 5 mass% to 8 mass%. However, the values of the U.T.S. were reduced when the Ni content was over 8 mass%. The mechanical strength of the interface between the substrate and the modified area is stronger in comparison with that of the substrate alloy. (3) Fracture cracking initialtion is observed around the coarse Al3Ni(β) intermetallic particles. Based on the examined data, the optimum Ni content in the modified 5052 alloy was determined to be 5 to 8 mass%.
