Refining whisker size of 2024Al/Al₁₈B₄O₃₃w composite through extrusion and its effects on the material's micro-structures and mechanical properties

Hot extrusion is used to improve the distribution of whiskers and refine the whisker sizes of 2024Al/Al₁₈B₄O₃₃w composite. The grain size and the ultimate tensile strength of the extruded 2024Al/Al₁₈B₄O₃₃w composite are analyzed. The results show that the average length of whiskers decreases due to the whisker breakage. The nonuniform distributions of stress and velocity along the whisker lead to whisker breakage. The microcrack between the broken whiskers can propagate into the interface or the matrix, related to the wedge angle of the broken whisker. The extrusion is beneficial to the whisker staggered and makes it easy for the microcracks filled with matrix. The whisker breakage and the whisker staggered result in the decreasing distance between the neighboring whiskers. Due to the dislocation motion constrained by matrix and the overlap of the deformation areas, the decreasing distance between the neighboring whiskers promoting the recrystallization results in the smaller grain size. During tensile tests, due to the smaller resistance with the smaller distance between the neighboring whiskers, the cracks between the progressive broken whiskers are easy to coalesce resulting in the lower ultimate tensile strength of the extruded composite.