Al3Cu

Al₃Cu is an intermetallic compound formed in aluminum-copper systems, representing a hard, brittle phase that appears as a constituent in cast aluminum alloys and precipitation-hardened aluminum-copper alloys. This phase is significant in aerospace and automotive casting applications, where it forms during solidification and contributes to strength through precipitation hardening; however, its brittleness means engineers typically manage its presence rather than rely on it as a primary strengthening phase. Al₃Cu is notable as the primary hardening precipitate in classical 2xxx-series aluminum alloys (such as 2024), where controlled precipitation of this phase enables high strength-to-weight ratios critical for aircraft structures.