Effect of a whisker surface treatment on the strength of Al₁₈B₄O₃₃ whisker reinforced AC4CH aluminum alloy composites

A new surface treatment method for aluminum borate whisker was developed in order to suppress the interfacial reaction between the whisker and aluminum alloy. By depositing Mg on the whiskers under 10 Pa at 650°C for 3.6 ks, and heating them in air at 800°C for 1.8 ks, a uniform MgAl₂O₄ layer with a thickness of 10-20 nm covered the whisker. MgAl₂O₄ layer had a close bonding to the whisker. No treatment whisker, SiO₂ binder added whisker, Mg coated whisker and MgAl₂O₄ coated whisker reinforced AC4CH aluminum alloy composites were fabricated by squeeze casting, respectively. Compressive strength of the whisker preforms having Mg coat and MgAl₂O₄ coat increased remarkably. The deformation of the preform was avoided during squeeze casting. Tensile strength of Mg coat whisker reinforced composites did not decrease, and that of MgAl₂O₄ coat whisker reinforced composites was enhanced by 37% after aging treatment (T6). The interface having MgAl₂O₄ coat showed a stable state. MgAl₂O₄ coat can be regarded as a good barrier to prevent the interfacial reaction between aluminum borate whisker and aluminum alloy matrix.