Meaning
Intermetallic compounds form during the thermal processing of aluminum and copper joints in battery busbars. The al2cu phase specifically designates the theta phase which develops as a brittle layer at the junction between these two metals. Excessive growth of this material reduces the mechanical toughness of the connection while simultaneously increasing electrical resistance across the bond area.
It limits the operational lifespan of welded tabs if the thickness of the layer exceeds common engineering tolerances.
Growth Condition
Thermal exposure during laser or ultrasonic welding accelerates the diffusion of aluminum atoms into the copper lattice. This migration creates a stratified interface where the al2cu phase appears alongside other stoichiometric variations. High temperatures sustain the atomic movement required to expand the thickness of the brittle region.
Mechanical Constraint
Brittleness within the joint interface creates a specific vulnerability to vibrational fatigue. Because the al2cu phase has lower fracture toughness than either base metal, it acts as a primary location for crack initiation under cyclic loading. Joints containing thick layers fail suddenly rather than deforming elastically.
Resistance Modification
Electrical throughput suffers as the intermetallic layer expands. The al2cu phase exhibits higher bulk resistivity than the pure copper or aluminum it replaces. Voltage drops across the interface increase linearly with the thickness of the theta phase region.
