Abstract: A steel/aluminum welded structure comprises a hot-dip Al-coated steel sheet 1 spot welded with an aluminum or aluminum alloy sheet 2. The steel sheet 1 is coated with a coating layer 4 containing, by mass, 3-12% of Si and 0.5-5% of Fe. An area ratio of an Al—Fe binary alloy layer, formed at the joint boundary, is controlled to 90% or less. An unalloyed region 9 exists between an Al—Fe—Si ternary alloy layer 6 at an interface of a steel substrate 5 with the coating layer 4 interface and the Al—Fe binary alloy layer at the joint boundary. A steel substrate 5 preferably contains 0.002-0.020% of N for formation of a N-enriched surface layer in contact with the coating layer 4. The N-enriched layer impedes propagation of the brittle Al—Fe binary alloy layer to the whole of the joint boundary and raises joint strength of the steel/aluminum welded structure.

Abstract: A steel/aluminum welded structure comprises a hot-dip Al-coated steel sheet 1 spot welded with an aluminum or aluminum alloy sheet 2. The steel sheet 1 is coated with a coating layer 4 containing, by mass, 3-12% of Si and 0.5-5% of Fe. An area ratio of an Al—Fe binary alloy layer, formed at the joint boundary, is controlled to 90% or less. An unalloyed region 9 exists between an Al—Fe—Si ternary alloy layer 6 at an interface of a steel substrate 5 with the coating layer 4 interface and the Al—Fe binary alloy layer at the joint boundary. A steel substrate 5 preferably contains 0.002-0.020% of N for formation of a N-enriched surface layer in contact with the coating layer 4. The N-enriched layer impedes propagation of the brittle Al—Fe binary alloy layer to the whole of the joint boundary and raises joint strength of the steel/aluminum welded structure.

Abstract: A molten zinc alloy, which contains 4–22 mass % Al, 1–7 mass % Mg and optionally one ore more of Ti, B and Si at very small ratios, is held at a temperature Th higher than (a solidification-beginning temperature Ts.b.+85° C.) for homogenization, and then cooled down to a temperature Tc equal to (Ts.b.+20–65° C.). After the molten alloy is poured in a mold, it is naturally cooled and solidified to an ingot, while its upper part is being heated. Once an upper surface of the zinc alloy in the mold begins to solidify, it is optionally cooled with water. The produced ingot has a structure without cracks or cavities, so that it is safely fed to a molten pool for replenishment.

Abstract: A molten zinc alloy, which contains 4-22 mass % Al, 1-7 mass % Mg and optionally one ore more of Ti, B and Si at very small ratios, is held at a temperature Th higher than (a solidification-beginning temperature Ts.b.+85° C.) for homogenization, and then cooled down to a temperature Tc equal to (Ts.b.+20-65° C.). After the molten alloy is poured in a mold, it is naturally cooled and solidified to an ingot, while its upper part is being heated. Once an upper surface of the zinc alloy in the mold begins to solidify, it is optionally cooled with water. The produced ingot has a structure without cracks or cavities, so that it is safely fed to a molten pool for replenishment.

Abstract: Degradation of the surface luster of a hot-dip Zn—Al—Mg plated steel sheet is inhibited by controlling the contact temperature between the plating layer and a water stream in a water cooling step after plating layer solidification, thereby suitably controlling the strip temperature during contact with the water stream, and further by incorporating a small amount of a suitable readily oxidizing element in the plating bath to stabilize the oxidation state of the plating surface layer Al and Mg.

Abstract: A hot-dip Zn—Al—Mg plated steel sheet good in corrosion resistance and surface appearance that is a hot-dip Zn-base plated steel sheet obtained by forming on a surface of a steel sheet a hot-dip Zn—Al—Mg plating layer composed of Al: 4.0-10 wt. %, Mg: 1.0-4.0 wt. % and the balance of Zn and unavoidable impurities, the plating layer having a metallic structure including a primary crystal Al phase or a primary crystal Al phase and a Zn single phase in a matrix of Al/Zn/Zn2Mg ternary eutectic structure. To obtain a plating layer possessing this metallic structure, the cooling rate of the plating layer adhering to a steel strip extracted from a plating bath and the plating bath temperature are appropriately controlled in a continuous hot-dip plating machine and/or appropriate amounts of Ti and B are added to the bath.

Abstract: A hot-dip Zn—Al—Mg plated steel sheet good in corrosion resistance and surface appearance that is a hot-dip Zn-base plated steel sheet obtained by forming on a surface of a steel sheet a hot-dip Zn—Al—Mg plating layer composed of Al: 4.0-10 wt. %, Mg: 1.0-4.0 wt. % and the balance of Zn and unavoidable impurities, the plating layer having a metallic structure including a primary crystal Al phase or a primary crystal Al phase and a Zn single phase in a matrix of Al/Zn/Zn2Mg ternary eutectic structure. To obtain a plating layer possessing this metallic structure, the cooling rate of the plating layer adhering to a steel strip extracted from a plating bath and the plating bath temperature are appropriately controlled in a continuous hot-dip plating machine and/or appropriate amounts of Ti and B are added to the bath.