What method is typically used to harden aluminum alloys in aircraft construction?

Heat treatment is the correct method typically used to harden aluminum alloys in aircraft construction. This process involves heating the aluminum alloy to a specific temperature, holding it there for a predetermined duration, and then rapidly cooling it. The heat treatment process alters the microstructure of the aluminum, resulting in increased strength and improved material properties.

In the context of aircraft construction, aluminum alloys are often used due to their favorable strength-to-weight ratio, and heat treatment enhances these characteristics. Different aluminum alloys react differently to heat treatment, which can include processes like solution heat treatment and aging (either natural or artificial).

Other methods such as cold working can improve strength through deformation, but they do not change the inherent material properties to the same extent as heat treatment. Electroplating and surface hardening techniques do not significantly affect the bulk properties of the metal but instead enhance surface characteristics such as corrosion resistance or wear resistance. Therefore, heat treatment remains the primary method for hardening aluminum alloys utilized in aviation.