Observations on the Effect of Alloy Composition on Metal Flow and Defect Formation in Aluminum Lost Foam Castings

摘要

Several synthetic and commercial aluminum alloys were used to produce lost foam castings. The synthetic Al-Si alloys were poured at a constant superheat, rather than at a constant pouring temperature. For the synthetic Al-Si alloys, varying in composition from 1 percent Si to 12.3 percent Si, the metal front velocity was highest for the long freezing range 1 percent Si alloy and was nearly constant for compositions of 6 percent to 12.3 percent Si. These results are somewhat different compared with previous research, probably because the previous work used a constant pouring temperature and hence different superheats. As the silicon content increased, the number of internal pores increased dramatically while the severity of blister defects decreased, similar to what has been observed previously. However the folds were nearly the same for all compositions. The fillability, metal front velocity, and defect severity for three commercial alloys-319, 356, and 206-were measured and compared. Although the liquidus temperature of 206 alloy is nearly 50 percent C (90 deg F) higher than for the other alloys, the fillability of the 206 alloy was nearly identical to that for the 319 and 356 alloys when a constant superheat was used. In most tests, the metal front velocity was higher for the 206 alloy, particularly for very thin sections and when a constant superheat was used. Pyrolysis defects, such as folds, were slightly more likely to form when the 206 alloy was used to produce the castings.