Effect of hydrogen- and oxygen-containing heterogeneities on the tensile strength of solid and molten aluminum

Abstract

Low tensile strength of aluminum melt is a problem for traditional casting and additive manufacturing, while the tensile strength of solid aluminum is relevant for its application. Heterogeneities are considered as the main reason of decrease in the tensile strength, and investigation of their influence is a topical problem. We perform MD study of the effect of alumina inclusions, hydrogen bubbles and dissolved hydrogen on the tensile strength of aluminum in both solid and molten states. It is shown that uniformly dissolved hydrogen itself does not alter the tensile strength in most cases. An admixture of alumina can halve the tensile strength of solid aluminum, but in the case of a melt, the decrease in strength is only about 10% and even less at high temperatures. The most reducing the melt strength is the presence of non-collapsing bubbles stabilized by gas phase of hydrogen inside them. The tensile strength of the melt with hydrogen bubbles drops down in more than 10 times and even down to zero at high temperatures in comparison with the homogeneous melt for the total hydrogen concentration of about 1.4 at. %. Decrease in the hydrogen content leads to squeeze of the initial bubbles and increases the tensile strength. In the case of solid aluminum, the effect of hydrogen-filled bubbles does not depend on the hydrogen content and is equal to the effect of empty pores or alumina inclusions of the same size. Almost zero tensile strength of aluminum melt at casting and other technological processes can be explained by the combination of the admixture of hydrogen in the metal and spatial heterogeneities of the melt flow, which results in the hydrogen-stabilized bubbles tearing the melt at tension.