Effect of Ti/B Additions on the Formation of Al₃ Ti of in situ TiB₂/Al Composites

A novel technique for fabricating TiB₂/Al composites in molten aluminum was introduced. The formation mechanism of brittle Al₃Ti particulates up to 30 m in size produced in the composites was studied and a method of eliminating them was proposed. The results show that (1) the brittle Al₃Ti particulates are always present in the composites when the molar ratio of Ti to B n_Ti:n_B is 1:2; and (2) the formation of the brittle Al₃Ti phase can be avoided entirely from the final product by using a proper n_Ti:n_B of l:4 in the Ti-B-Al preforms.In the former case, the tensile elongation of the composite is only 4%, much lower than the value of pure aluminum (20%). In the later case, the tensile elongation of this composite is 10%, higher than the value of the composite with a lot of Al₃Ti (4%), whereas the ultimate tensile strength of the former is nearly that of the later.