Nisshin Steel Co., Ltd.

Atsushi Andoh

Atsushi Komatsu

Takao Tsujimura

Toshiharu Kittaka

Kouichi Watanabe

Nobuhiko Yamaki

Yasuhiro Yamamoto

Yasunori Hattori

Tadaaki Miono

Seiji Sasabe

Tetsu Iwase

Katsuyuki Takezaki

Yasutaka Kawaguchi

Ryuuji Ninomiya

A steel/aluminum welded structure comprises a hot-dip Al-coated steel sheetspot welded with an aluminum or aluminum alloy sheet. The steel sheetis coated with a coating layercontaining, by mass, 3-12% of Si and 0.5-5% of Fe. An area ratio of an Al&#x2014;Fe binary alloy layer, formed at the joint boundary, is controlled to 90% or less. An unalloyed regionexists between an Al&#x2014;Fe&#x2014;Si ternary alloy layerat an interface of a steel substratewith the coating layerinterface and the Al&#x2014;Fe binary alloy layer at the joint boundary. A steel substratepreferably contains 0.002-0.020% of N for formation of a N-enriched surface layer in contact with the coating layer. The N-enriched layer impedes propagation of the brittle Al&#x2014;Fe binary alloy layer to the whole of the joint boundary and raises joint strength of the steel/aluminum welded structure.

Steel/aluminum welded structure

A molten zinc alloy, which contains 4&#x2013;22 mass % Al, 1&#x2013;7 mass % Mg and optionally one ore more of Ti, B and Si at very small ratios, is held at a temperature Thigher than (a solidification-beginning temperature T+85&#xb0; C.) for homogenization, and then cooled down to a temperature Tequal to (T+20&#x2013;65&#xb0; 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.

Method of manufacturing zinc alloy ingot

Degradation of the surface luster of a hot-dip Zn&mdash;Al&mdash;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.

Hot-dip Zn plated steel sheet excellent in luster-retaining property and method of producing the same

A hot-dip Zn&mdash;Al&mdash;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&mdash;Al&mdash;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/Zn Mg 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. Occurrence of a stripe pattern peculiar to this plated steel sheet is controlled by morphology control of a Mg-containing oxide film up to solidification of the plating layer or by adding an appropriate amount of Be to the plating bath.

Hot-dip Zn-A1-Mg plated steel sheet good in corrosion resistance and surface appearance and method of producing the same

A hot-dip Zn&mdash;Al&mdash;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&mdash;Al&mdash;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/Zn,Mg 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. Occurrence of a stripe pattern peculiar to this plated steel sheet is controlled by morphology control of a Mg-containing oxide film up to solidification of the plating layer or by adding an appropriate amount of Be to the plating bath.

Hot-dip Zn-Al-Mg coated steel sheet excellent in corrosion resistance and surface appearance and process for the production thereof

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Sakai, Japan

Atsushi Andoh