Corrosion behaviour of as-cast ZK40 with CaO and Y additions

The microstructures of as-cast ZK40, ZK40 with 2% (mass fraction) CaO and ZK40 with 1% (mass fraction) Y were investigated, and the intermetallic phase morphology and the distribution were characterised. By having discrete intermetallic particles at the grain boundaries for the ZK40, the microstructure was modified to a semi-continuous network of intermetallic compounds along the grain boundaries for the ZK40 with CaO or Y additions. The CaO was not found in the microstructure. However, Ca was present in Ca$_2$Mg$_6$Zn$_3$ intermetallic compounds which were formed during casting. Hydrogen evolution and electrochemical impedance spectroscopy tests revealed that the addition of CaO slightly enhanced the corrosion resistance whereas Y had a negative effect on the corrosion resistance of ZK40. Immersion tests showed that severe localised corrosion as well as corrosion along the intermetallic compounds played an important role in the corrosion process of ZK40–Y whereas the localised corrosion was not pronounced for ZK40 or ZK40–CaO alloys. Micro-segregation in the α-Mg matrix was notably higher for the ZK40 alloy compared with the modified alloys. The combination of this effect with a possible formation of a more stable corrosion layer for the ZK40–CaO was attributed as the main reason for an improved corrosion resistance for the ZK40–CaO alloy

Microstructure evolution of Mg-11Gd-4.5Y-1Nd-1.5Zn-0.5Zr (wt%) alloy during deformation and its effect on strengthening

Microstructure and texture evolutions during tensile and compression deformation of an as-extruded Mg–11Gd–4.5Y–1Nd–1.5Zn–0.5Zr (wt%) alloy have been investigated using in-situ synchrotron radiation diffraction and subsequent microscopy. The alloy consists of 〈View the MathML source101¯0〉 fiber texture, {View the MathML source112¯0}[0001] and {View the MathML source112¯0}〈View the MathML source101¯0〉 texture components prior to deformation. The texture evolves from [0001] to 〈View the MathML source101¯0〉 in tension, but from 〈View the MathML source101¯0〉 to [0001] in compression. The evolution of texture is attributed to the activity of the tensile twinning and non-basal 〈a〉 type slip. The tendency of texture evolution depends on the favorable texture component for the activation of above deformation modes. The grain refinement, Mg5(Gd, Y, Nd) and LPSO phases, and the texture contribute to the improvement in strength.The authors thank Dr. Jan Bohlenand Dr. Sangbong Yi for their fruitful discussion. Prof. Florian Pyczak and Mr. Uwe Lorenzare acknowledged for the provision of access to the TEM facilities at Helmholtz-Zentrum Geesthacht. The access to the beam line PETRA III at DESY, Hamburg, Germany was provided under the proposal number I-20130153,andtheworkofN. Schellis greatly appreciated. This work is supported by the National Key Technologies R&D Program(2012BAE01B04,2012DFH50100,KGFZD-125-13-021,201001C0104669453). Zijian Yu would like to thank the Chinese Academy of Sciences and German Academic Exchange Service (CAS-DAAD)scholarship program (Grant Number: A/12/94735)for the financial support