1. School of Material Science and Engineering Lanzhou University of Technology No. 287 Langongping Road Qilihe District Lanzhou 730050 P. R. China
2. State Key Laboratory of Advanced Processing and Recycling of Nonferrous Metals Lanzhou University of Technology Lanzhou 730050 P. R. China
3. School of Materials Engineering Lanzhou Institute of Technology Lanzhou 730050 P. R. China