| Summary: | 碩士 === 中山醫學大學 === 職業安全衛生學系碩士班 === 105 === The traditional arc welding process has several advantages with low cost, time efficiency and easy access. However, defects of segregation, porosity, cracks and slags would be formed and the joining strength was then degraded for the arc welding applied to join the metal matrix compositions (MMCs). The hot pressing is a solid state bonding process that could be used to join the MMCs below the melting point of the metal matrix, and then defects for the arc welding used to join MMCs would be avoided. To obtain a sound joint with sufficient strength, the low melting point of zinc was added to filler and the hot pressing were conducted to join Al/(SiC)p MMCs in this work.
The 30 μm in mean particle size of aluminum powder and 40 μm in mean particle size of silicon carbide were slected to fabricate the Al/(SiC)p MMC. The main parameters of Al/(SiC)p MMC were 400℃ in sintering temperature, 400 MPa in sintering pressure and 30 minute in sintering duration. Then zinc was added to Al/(SiC)p mixed powder from 0 wt.%- 40 wt.% as the filler. The bonding temperature of 420℃- 600℃, 220 MPa of bonding load, and bonding duration was set from 30- 120 minute to join the Al/(SiC)p MMCs using hot pressing process. The microstructure and mechanical properties were determined to evaluate bonding performance of Al/(SiC)p MMCs.
The melting point of metal matrix decreased with increasing the zinc content in the filler due to eutectic bonding was formed between the aluminum and the zinc. A sound joint with the high bonding strength was achieved for the filler with zinc was used to join Al/(SiC)p MMCs. Neither cracks nor delaminations were found at bonding interface and the eutectic reaction can be found in the microstructure. The optimum content of zinc in the filler was 20 wt% in this work. The crack was found in the bonding interface between the Al/(SiC)p MMC and the filler when the content of zinc exceeded 40 wt%. A high level oxygen can be found near the crack, indicating the zinc oxide would lead the crack to form and the bonding performance was degraded. Extending bonding duration resulted in grain coarsening and then degraded in bonding strength and hardness. The bonding performance was improved significantly when the elevated bonding temperature was used to join Al/(SiC)p MMCs. An elevated boning temperature provided sufficient thermal energy to make a sound bonding between the metal matrix and the SiC enforcement. A great bonding performance of Al/(SiC)p MMCs can be achieved by the hot pressing process combined the filler with a low melting point of zinc content.
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