Aging behavior of an in-situ TiB2/Al-Cu-Li-x matrix composite

Transmission electron microscopy, differential scanning calorimetry and hardness tests have been performed on an in-situ TiB2/Al-3.3Cu-1.0Li-0.60Mg-0.40Ag-0.14Zr-0.13Si composite to study its aging behavior at 175 °C. A cubic phase suspected to be the σ (Al5Cu6Mg2) phase or its variant is precipitated at all aging stages studied, and this phase is not typically observed in the Al-Cu-Li alloys. The primary hardening (aging for 3 h) phases consist of δ′ (Al3Li), β′ (Al3Zr) and the cubic phase. After aging for 18 h, all precipitates including T1 (Al2CuLi), S (Al2CuMg), θ′ (Al2Cu), δ′, β′ and the cubic phase have appeared, and the formation of T1 and S results in a rapid increase in hardness. With prolonging of aging time, the apparent coarsening of T1 and S results in a decline in hardness.