Microstructural development during friction stir welding of work hardenable Al-Mg alloys

Intermetallic particle and grain size distributions throughout the regions of friction stir welds in the work hardenable Al-Mg alloy 5251 have been quantified using optical and scanning electron microscopy. High temperature differential scanning calorimetry has been used to quantify the variation in stored energy across the various weld regions, which has been related to variations in the basemetal Mg2Si and Al-x(Fe,Mn)(y)Si-z inclusion populations and grain size distributions. The thermomechanical modification of particles and basemetal recrystallisation through heat affected and thermomechanically affected zones has thus been determined along with banding effects in the basemetal and verified using Gleeble simulations. The effect of spatially inhomogeneous intermetallic phases on matrix grain structure development and banding (so-called onion rings), has been identified as has the critical heating rate needed for recrystallisation without recovery.