Method for welding a zinc coated steel sheet

A lap-joint welding method of welding a first zinc coated steel sheet and a second zinc coated steel sheet stacked to partially overlap the first zinc coated steel sheet using a welding wire, to reduce a porosity defect of welded metal, comprising:

• welding, wherein the welded metal has a pore area ratio of 0.97% or less and have a tensile strength of 700 MPa or more,
• wherein a gap of a welded joint formed by the method is 0 mm,
• wherein the welding current is supplied as a bidirectional pulse current in which positive direct current and negative direct current are of equal and constant absolute value in a range from 200 A to 270 A, and
• wherein a welding polarity is alternately altered to satisfy a welding polarity fraction, in a range of 0.25 to 0.35, the welding polarity being defined by
• ENR,%/(EPR,%+ENR,%)
• where, ENR, % is a fraction of time for which current through the welding wire is negative direct current, and EPR, % is a fraction of time for which current through the welding wire is positive direct current.