Strengthening of dislocation and precipitation for high strength and toughness casting Al–Zn–Mg–Cu alloy via trace TiB2+TiC particles

Abstract

Adding alloying elements to increase precipitation is a common method to strengthen aluminum (Al) alloys, but an excessively high alloying element content causes segregation and a reduction in plasticity. In this work, the tradeoff between alloying element content and segregation was explored along with the simultaneous increase in precipitation and dislocation density under the action of trace TiB2+TiC particles with the aim of giving a full play to the strengthening effect of dislocation and precipitation and maximizing the strength and toughness of the alloy. The cast Al–Zn–Mg–Cu alloys contained various alloying elements (Zn, Mg), and the alloys were reinforced with 0.5 wt% TiB2+TiC particles via in-situ reaction in the Al melt. The TiB2+TiC particles blocked the diffusion of the alloying elements and inhibited segregation, promoting solution of alloying elements and yielding dispersed and finer precipitates after solution and aging. Meanwhile, owing to the difference in the thermal expansion coefficients of the matrix and particles, the dislocation density of the alloy doubled. Therefore, the yield strength, elongation, and the product of the tensile strength and elongation of the Al-6.60Zn-3.15Mg-1.60Cu alloy with particles reinforcement were 562 MPa, 4.5%, and 3163 MPa·%, respectively, representing increases of 31.6%, 108.9%, and 186.0%, respectively, compared with the cast 7075 alloy. This study is significant for the successful preparation of high-strength and high-toughness cast aluminum alloys with high alloying-element content.