한국주조공학회

Effect of surface roughness and microstructure of the specimen on tensile properties of Ni-Al bronze casting has been inves- tigated. Surface roughnesses of the tensile test specimen of interest are in range of 0.1 to 2.0 um in Ra obtained by changing machining conditions. Fracture of the Ni-Al bronze casting initated at the surface and propagated in a brittle manner during ten- sile tests. Tensile elongation value of the casting was strongly dependent on the surface roughness range studied, while tensile and yield strengths were almost independent on it. The elongation value was almost constant up to the surface roughness of 1.0 um in Ra, and then decreased in a linear manner with an increase in Ra value up to 2.0 um. However, tensile strength and hardness were strongly dependent on the rnicrostructure, especially 0: phase fraction, and were decreased with increasing 05 phase fraction in microstructure. It is, therefore, recommended that decrease of surface roughness up to 1.0 pm in Ra, shrinkage porosity and at phase are required in order to obtain good tensile properties for Ni-Al bronze casting.