Metal member having a coated surface of zinc and its anticorrosive coating chromium-rust surface treatment agent for metal member having a surface of zinc

Zinc surface of a metal member, hardly occur cracking and peeling problems, discloses a non-chromium anticorrosive surface treatment agent to form a siliceous film to impart good anti-rust performance. Chromium-rust surface treatment agent is an alcoholic solution of alkoxysilane oligomer having a weight average molecular weight of 1,000 to 10,000, 2.5 to 15% of silicon in the alkoxysilane oligomer molecule is replaced with titanium there. To obtain a partially alkoxysilane oligomer obtained by substituting titanium, it is reacted with a titanium compound chelated approximately half of the alkoxy groups of the titanium tetraalkoxide with tetraalkoxysilane monomer or alkoxysilane oligomer with an alcohol solution.