Melt treatment effects on porosity and impact strength in hypoeutectic aluminum silicon alloy

The effects of the three factors (modification, grain refinement, and hydrogen level) on the amount of porosity, impact strength, and performance of the reduced pressure test in A356 alloy have been studied. It was found that grain refinement, acting singly and in combination with modification, reduces the porosity by inducing mass feeding. However, this beneficial effect may not be found at all cooling rates and casting sizes. There is less total shrinkage in Sr-alloyed samples than in those which are non Sr-alloyed. The reason for this is supposed to be a difference in the liquid density which may be higher in Sr-alloyed samples. Modification has the strongest effect on improving the impact strength of A356 alloy. Hydrogen reduces it slightly. On the other hand, grain refinement, acting singly or in combination with modification, was not found to improve the impact strength of the alloy. To obtain optimum impact strength, it is recommended that a combination of modification and degassing to about 0.1 ml.H$ sb2$/100 g. Al. be used. An excellent linear relatiosnhip between density and hydrogen level exists for all combinations of melt treatment processes when the redued pressure test is used. Three methods of predicting the true hydrogen level are proposed and calculated hydrogen levels agree reasonably well with measured melt hydrogen within the error range of $ pm$0.05-0.1 ml./100 g. Al