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We investigated the twinning and detwinning behavior of { 10(1)2} twins in pre-compressed pure Mg and Mg alloys AZ31 and AZ91 by tensile tests,in situ electron-backscattering diffraction,and high-resolution transmission electron microscopy.The solute elements Al and Zn were found to disrupt the synchronous migration of atoms on the twin boundary during twinning formation,yielding more incoherent twin boundaries.The low-angle boundaries were formed on the primary twin boundaries after detwinning,and its fraction increased markedly with increasing solute-element concentration,due to increased incoherent twin boundaries in Mg alloy.It was easier to form the secondary {10(1)2} twins in the primary {10(1)2} twins accompanied by detwinning in alloy with higher solute-element concentration possibly owing to the low mobility of the incoherent twin boundary and the variation of local stress state by precipitates in the Mg alloys.Moreover,the ultimate tensile strength increased more substantially in the Mg alloys subjected to the pre-compression,especially the AZ91 alloy,which is attributed to the hardening effects caused by low-angle and secondary twin boundaries and to the reduced Schmid factor for the basal slip in Mg alloys during detwinning.