Grain Structure Evolution in 6013 Aluminum Alloy during High Heat-Input Friction-Stir Welding

Area of Science:

• Materials Science
• Metallurgy
• Welding Engineering

Background:

• Friction-stir welding (FSW) is a solid-state joining process.
• Microstructural evolution under extreme welding conditions requires further investigation.
• High-heat input FSW parameters can significantly alter material properties.

Purpose of the Study:

• To evaluate the impact of high-heat input FSW on the microstructural evolution of 6013 aluminum alloy.
• To understand the unusual structural responses under extreme deformation conditions (high strain, temperature, strain rate).
• To investigate the formation of specific microstructural features and the recrystallization behavior.

Main Methods:

• Utilized a commercial 6013 aluminum alloy.
• Performed friction-stir welding (FSW) at a high spindle rate (1100 rpm) and low feed rate (13 mm/min).
• Employed a titanium alloy (Ti-6Al-4V) backing plate to manage heat loss.

Main Results:

• Observed the formation of a distinct fine-grained layer at the upper weld surface, attributed to the FSW tool's shoulder stirring action.
• Documented the retardation of continuous recrystallization.
• Explained the recrystallization retardation by the competition between recovery and recrystallization at elevated temperatures, where recovery reduces dislocation density.

Conclusions:

• High-heat input FSW promotes the formation of fine grains via tool stirring.
• The interplay between recovery and recrystallization at high temperatures significantly influences the microstructural development during FSW.
• Understanding these mechanisms is crucial for optimizing FSW processes for aluminum alloys.