Kink Bands and Strengthening of Millefeuille-Structured Magnesium Alloys by Cluster-Arranged Nanoplates (CANaPs): The Case of Mg-0.4Zn-1.0Y Alloy

The paper reports the development of a high-strength magnesium alloy in an Mg-Zn-Y system, strengthened by pseudo-2D arrangements of ordered nanoclusters in a solid solution matrix. Designated as cluster-arranged nanoplates (CANaPs), it is composed of L12-ordered Zn6Y8 clusters arranged in layers (cluster-arranged layers or CAL) separated by a random number of basal planes of magnesium with no long-range order. The CAL consists of four layers of fcc stacking (ABCA). The CANaP evolves from a hot pressed and solutionized rapidly solidified alloy during aging. We identify this new arrangement as a part of the millefeuille structure (MFS) family due to the harder transition metal-rare earth-segregated layers separated by softer layers of magnesium planes. The CANaPs thicken with time and temperature by acquiring more CALs. However, the CANaP dispersion decreases with time following an initial increase. The presence of CANaPs in a heat-treated alloy improves the tensile strength only moderately. However, on hot extrusion following heat treatment, kink bands form that can be correlated with the dispersion of CANaPs in the pre-extruded alloy. The yield stress of the extruded alloy significantly improves and can be correlated with kink band dispersion. The maximum yield stress achieved is 368 MPa with an elongation of 10.5%, comparable to the strength of 375 MPa achieved in the LPSO-strengthened Mg-1.0Zn-2.0Y alloys with virtually no difference in specific yield strength.