中国有色金属学报(英文版)
Transactions of Nonferrous Metals Society of China
| Vol. 28 No. 3 March 2018 |
（1. Magnesium Innovation Centre, Helmholtz-Zentrum Geesthacht, Max-Planck-Strasse 1, D 21502, Geesthacht, Germany; 2. Institute of Materials Science, Joining and Forming, Graz University of Technology, Kopernikusgasse 24/I, 8010 Graz, Austria; 3. Departamento de Ciencia de Materiales, Facultad de Ciencias Químicas, Universidad Complutense, Av. Complutense, s/n, 28040 Madrid, Spain; 4. Brunel Centre for Advanced Solidification Technology, Brunel University London, Uxbridge, Middlesex, UB8 3PH, UK; 5. Department of Materials Engineering, University of Sao Paulo, Av. Joao Dagnone, 1100 Jd. Sta Angelina, 13563-120, Sao Carlos, Brazil）
Abstract: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 Ca2Mg6Zn3 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.
Key words: Mg alloy; ZK40; Y addition; CaO addition; corrosion behaviour
