Steel material coated with Zn-Al alloy-Mg-Si is highly resistant to corrosion and process for producing

A steel material coated with an alloy of Zn-Al-Mg-Si with excellent resistance to corrosion, wherein the alloy coating Zn-Al-Mg-Si comprises (percentages by weight): At least 45 % and not more than 70% Mg least 3% and less than 10% if at least 3% and less than 10%, and optionally one or more elements selected from the group consisting of 0.01-1.0% in 0.1-10.0% Sn 0.01-0.5% Ca Be 0.01-0.2% Ti 0.01-0.2% Cu 0.1-1.0% Ni 0.01- 0.2% Co 0.01-0.3% Cr 0.01-0.2% Mn 0.01-0.5% Fe 0.01 to 3.0% 0.01-0.5% Sr being the remainder Zn and unavoidable impurities, wherein the ratio of Al / Zn is from 0.89 to 2.75 and the coating layer contains a flaky Mg2Si phase having a ratio of the short diameter to the long diameter less than 0.4 , observed in a polished cross section at an angle of 5 °.