How does the addition of copper to aluminum alloys affect their strength and ductility?

Adding copper to aluminum alloys significantly increases their strength, particularly in the form of tensile and yield strength. Copper acts as a hardening agent, creating a more rigid structure within the alloy. However, this increase in strength often comes at the expense of ductility. As copper content rises, the ductility of the aluminum alloy decreases because copper reduces the alloy's ability to deform under stress without fracturing. The balance between strength and ductility is crucial in alloy design, as higher strength alloys may be less suitable for applications requiring formability and flexibility.