Zn-al-mg-si coated steel sheet

A Zn—Al—Mg—Si coated steel sheet comprising a base steel sheet and a coated layer formed on at least one surface of the base steel sheet, wherein

• the coated layer has a chemical composition containing, in mass %, Mg:
• 0.50% to 3.00%, Al:
• 0.10% to 3.00%, Si:
• 0.010% to 0.20%, and Fe:
• 0.30% or less, with the balance being Zn and inevitable impurity, and a Zn—Al—MgZn2 ternary eutectic alloy structure,
• in a reflected electron image at a magnification of 5000 times obtained by irradiating a surface of the coated layer with an electron beam at an accelerating voltage of 7.0 kV using a scanning electron microscope, needle-shaped Mg2Si alloy phase having a major axis length of 0.5 μm or more is present in the Zn—Al—MgZn2 ternary eutectic alloy structure at a number density of less than 100,000/mm2 (including 0/mm2),
• in a reflected electron image at a magnification of 5000 times obtained by irradiating a surface of the coated layer with an electron beam at an accelerating voltage of 15.0 kV using a scanning electron microscope, needle-shaped Mg2Si alloy phase having a major axis length of 0.5 μm or more is present in the Zn—Al—MgZn2 ternary eutectic alloy structure at a number density of 500/mm2 or more, and
• in a reflected electron image at a magnification of 5000 times obtained by irradiating a surface of the coated layer with an electron beam at an accelerating voltage of 15.0 kV using a scanning electron microscope, needle-shaped SiO2 oxide phase having a major axis length of 0.5 μm or more is present in the Zn—Al—MgZn2 ternary eutectic alloy structure at a number density of 100,000/mm2 or more.