Twin density and twin thickness evolution in sputtered Al-Mg alloys

Twinned Al-Mg alloys have been reported. However, the role of Mg solute in facilitating the formation of growth twins remains unclear. By using a precession-assisted crystal orientation mapping technique (PACOM) coupled with transmission electron microscopy (known as ASTAR), we examined the evolution of twin boundaries in Al, Al-1Mg, and Al-2.2Mg (at. %) films. The twinned grain fraction elevates with increasing film thickness until it reaches a peak when the film thickness is 120-160 nm. The Al-Mg alloys exhibited greater twinned grain fractions than pure Al. To investigate the fluctuation of twinned grain fraction, two types of twin boundaries were classified including intergranular and intragranular twins. The initial increase in twin density is attributed to the impingement of twinned grains during island coalescence and the twinned grains are more likely to survive during the grain growth process. Whereas the decrease in twinned grain fraction in thicker films is related to the removal of intragranular twins, and a lack of formation mechanisms of new twins.

Automated summary

The role of Mg solute in facilitating the formation of growth twins in twinned Al-Mg alloys remains unclear. The twinned grain fraction increases with increasing film thickness until it reaches a peak at 120-160 nm. Al-Mg alloys show higher twinned grain fractions compared to pure Al. The increase in twin density is attributed to the impingement of twinned grains during island coalescence and their higher survival rate during grain growth.