The role of in-situ Al3Ti formed during solidification in improving the high-temperature properties of Al–Cu alloy

Abstract

In this paper, in-situ Al3Ti-reinforced Al–Cu alloys were fabricated by Ti alloying and exhibit outstanding high-temperature properties. The results show that when the volume fraction of Al3Ti is 7.8 %, the ultimate strengths of the alloy can reach 203.9 MPa and 144.1 MPa at 300 °C and 350 °C, which are 31.0 % and 51.4 % higher than the base alloy, respectively. The analysis indicates that in addition to precipitation strengthening, dislocation strengthening, and load-transfer strengthening, low-angle grain boundaries also play an important role in improving the high-temperature properties of the alloy. When the Ti concentration in the alloy melt is high, Al3Ti grows into the two-dimensional lamellar dendrite with a complex structure and serves as the heterogeneous nucleation site of multiple α-Al cores, which results in the abnormal grain growth behavior and increase of low-angle grain boundaries. Moreover, fracture mechanism analysis suggests that the existence of Al3Ti increases the number of initial cracks, which increases the risk of splitting the matrix. The deformation behavior of Al3Ti is mainly controlled by twins, stacking faults, and dislocations. Under tensile stress, cracks first form in Al3Ti and then evolve into non-equiaxed voids in the matrix, which eventually connect and lead to the fracture of the alloy.