GATE MT 2019 Q8. During low strain rate (< or equal to 0.1 per second) deformation of a metal at room temperature, the one that deforms by twinning mode is :

Mg is the metal that can show relevant twins at lower strain rates.

Fe exists as BCC or FCC; Al & Ni as FCC and Mg as HCP. In crystals like BCC and FCC since there are more available slip systems the twinning doesn’t prominently occur at lower strain rates; this is because twinning doesn’t relive larger stress and slip systems are available for providing more relief; hence they mostly have twins in low T higher Strain rate.

Although high strain rate is still required for a considerable change in the deformation twins in HCP like Mg, due to its lower number of slip systems(only 3); slip can’t relive large stresses at low strain rates and thus twinning becomes the most prominent than slip that time. Also, the deformation, double twins can be active by only atomic displacement in HCP at lower strains however dislocation shifting also makes a criterion in FCC metals.

So, in short, we can say that most prominent twin is seen in Mg at lower strain rates.