1. F. Guo, P.L. Luo, Q. Bi and K. Li: Metal Materials and Metallurgy Engineering. Vol. 136 (2008), p.60.
2. G.I. Eskin: Ultrasonics Sonochemistry. Vol. 8(2001), p.319.
3. C.L. Zhang, M.S. Wu and H.W. Hao: Science and Technology. Vol. 6(2001), p.475.
4. Y. Cui, C. L. Xu and Q. Han: Scripta Materialia. Vol. l55(2006), p.975.
5. X.S. Leng, G.J. Zhang and L. Wu: Transactions of the China Welding Institution. Vol. 27 (2007), p.13.