Abstract:This work aimed to fabricate B₄C reinforced aluminum matrix composites via blended powder semisolid forming that is an implementation of the benefits of semisolid forming to the powder metallurgy. Al7075 elements were incrementally added to ethanol solution under mechanical mixing. Al7075 constituents and B₄C particles were blended in a high energy ball mill. Cold compacted Al7075/B₄C blends were pressed at semisolid state. The effects of the size of the matrix (20, 45 and 63 μm), reinforcing volume fraction (5%, 10% and 20%) and semisolid compaction pressure (50 and 100 MPa) on the morphology, microstructure, density, hardness, compression and bending strength were thoroughly analyzed. Experimental results revealed that the highest microstructural uniformity was achieved when large B₄C particles (45 μm) were distributed within the small particles (20 μm) of the matrix phase. Composites with matrix particles larger than reinforcing phase indicated agglomerations in loadings more than 10% (volume fraction). Agglomerated regions resisted against penetration of the liquid phase to the pores and lowered the density and strength of these composites. Composites with 20 μm Al7075 and 20% (volume fraction) 45 μm B₄C powder pressed under 100 MPa exhibited the highest values of hardness (HV 190) and compressive strength (336 MPa).

Key words: blended powder; mechanical alloying; semisolid forming; B₄C; aluminum matrix composite