Effect of TiC particles on the microstructure and properties of as-cast 7075‑based metal matrix composite

This study examines the effects of titanium carbide (TiC) particles on mechanical properties, microstructure, and the coefficient of linear thermal expansion of aluminum alloy 7075 in the as-cast state. Composite materials with a 7075 alloy matrix and TiC volume content ranging from 1 % to 7.5 % are fabricated using the stir casting technique with particles of average size 1.2 μm. Microstructural analysis using electron backscatter diffraction reveals the alloy grain refinement due to TiC additions. The grain size at the center of the casting decreases from 82 μm in the base alloy to 13 μm at 7.5 % TiC content, and the grain size gradient across the casting section decreases from 23 μm to 1 μm. Experimental results demonstrate a monotonic decrease of the linear thermal expansion coefficient from (22.6 ±1.6) ×10−6 K−1 for the base alloy to (21.5 ± 0.1) ×10−6 K−1 for the composite with 7.5 % TiC content for the temperature range of 20 – 200°C.  Addition of 1 % TiC to the 7075 alloy increases hardness from 68 ±1 to 74 ±1 MPa, yield strength from 96 ± 9 to 130 ± 4 MPa, and ultimate tensile strength from 174 ± 6 to 219 ± 20 MPa. Relative elongation remains almost unchanged with increasing TiC content up to 2.5 wt.%, maintaining a value of about 3 %. However, the further increase of reinforcement concentration leads to a sharp decrease in elongation to 1 % at 7.5 % TiC content.