The present invention relates to an ultra-high strength, hot-dip galvanized steel sheet having excellent surface quality and coating adherence and to a method for manufacturing thereof, the ultra-high strength, hot-dip galvanized steel sheet comprising: 0.1-0.3% by weight carbon (C); 0.1-2.0% by weight silicon (Si); 0.005-1.5% by weight aluminum (Al); 1.5-3.5% by weight manganese (Mn); 0.04% by weight or less phosphorus (P) (excluding 0% by weight); 0.015% by weight or less sulphur (S) (excluding 0% by weight); 0.02% by weight or less nitrogen (N) (excluding 0% by weight); the balance being Fe; and other inevitable impurities, and further comprising 0.01 wt.% to 0.07 wt.% of at least one kind of element selected from the group consisting of bismuth (Bi), tin (Sn) and antimony (Sb).

A method of forming a multilayered zinc alloy coating comprises steps of providing a bath of an aqueous electrolyte including zinc and a second electrodepositable component in an electrolytic cell having an anode and a cathode; applying a current or voltage between the anode and the cathode; modulating the applied current or voltage over time between at least two current or voltage values to thereby modulate the current density over multiple cycles between at least two current density values, wherein a first current density value is in a range of 0.3 to less than 2 A/dm.sup.2 and a second current density value is higher than the first current density value and is in a range of 0.6 to less than 5 A/dm.sup.2; and controlling the modulation of the applied current or voltage to obtain a multilayered structure having multiple layers of one or more of alternating proportions of the second component, alternating corrosion potential, alternating grain size, and alternating grain orientation, wherein one or more of the multiple layers has a thickness in the range of 1 to 10 μm.

A hot-dip plated steel according to one aspect includes a base steel and a hot-dip plating layer disposed on a surface of the base steel, a chemical composition of the hot-dip plating layer contains, by mass%, Al: 10.00% to 30.00%, Mg: 3.00% to 12.00%, Sn: 0% to 2.00%, Si: 0% to 2.50%, Ca: 0% to 3.00%, Ni: 0% or more and less than 0.25%, Fe: 0% to 5.00%, and the like, a remainder consists of Zn and impurities, a metallographic structure of the hot-dip plating layer contains 5 to 45 area% of an α phase having a grain diameter of 0.5 to 2 .Math.m, the metallographic structure of the hot-dip plating layer contains 15 to 70 area% of a MgZn.sub.2 phase, and, among the α phases having the grain diameter of 0.5 to 2 .Math.m, an area ratio of an α phase having a (111).sub.α//(0001).sub.MgZn2 orientation relationship to the adjacent MgZn.sub.2 phase is 25% to 100%.

A magnesium alloy composite structure includes a magnesium alloy substrate, a zinc layer applied to the magnesium alloy substrate, a copper layer applied to the zinc layer, a nickel strike layer applied to the copper layer; an autocatalytic nickel layer applied to the nickel strike layer and a surface layer applied to the autocatalytic nickel layer. Various surface layers include Aluminum Titanium Nitride, Boron Nitride, Chromium Nitride, Titanium Nitride, Zirconium Nitride, Zirconium Oxide, Zirconium Oxycarbide, Titanium Carbide, Titanium Nitride and Diamond Like Carbon.

A steel sheet for a fuel tank includes: a Zn—Ni alloy plated layer which is placed on one surface or each of both surfaces of a base metal and formed on at least one surface; and an inorganic chromate-free chemical conversion coating film which is placed over the Zn—Ni alloy plated layer. The Zn—Ni alloy plated layer has a crack starting from an interface between the Zn—Ni alloy plated layer and the inorganic chromate-free chemical conversion coating film and reaching an interface between the Zn—Ni alloy plated layer and the steel sheet, and a water contact angle on a surface of the inorganic chromate-free chemical conversion coating film is more than or equal to 50 degrees.

The present invention relates to a plated steel sheet, which can be used for vehicles, home appliances, construction materials and the like, and to a method for manufacturing the plated steel sheet.

The present invention relates to a hot-rolled steel sheet for a high strength galvanized steel sheet, having excellent surface quality, and a method for producing the same, the hot-rolled steel sheet comprising, by weight %: C: 0.05 to 0.15%, Si: 0.03 to 0.10%, Mn: 0.7 to 1.39%, P: 0.001 to 0.05%, S: 0.001 to 0.03%, Al: 0.002 to 0.035%, and the remainder being Fe and unavoidable impurities. The weight ratio of Mn/Si is 15 to 25, the weight ratio of C/Si is 1 to 5, and the weight ratio of Si/P is 3 to 10. The hot-rolled steel sheet has a microstructure consisting of, in area fraction, 10 to 40% of bainite, 20 to 30% of pearlite and 40 to 60% of ferrite, and includes a ternary eutectic compound of FeO, Fe.sub.2SiO.sub.4 and Fe.sub.3(PO).sub.4 formed within 50 μm from the surface.

A method for manufacturing a hot-rolled and coated steel sheet having a thickness between 1.8 mm and 5 mm. The method contains the steps of: providing a semi-product having a composition containing: 0.04%≤C≤0.38%, 0.40%≤Mn≤3%, 0.005%≤Si≤0.70%, 0.005%≤Al≤0.1%, 0.001%≤Cr≤2%, 0.001%≤Ni≤2%, 0.001%≤Ti≤0.2%, Nb≤0.1%, B≤0.010%, 0.0005%≤N≤0.010%, 0.0001%≤S≤0.05%, 0.0001%≤P≤0.1%, Mo≤0.65%, W≤0.30%, Ca≤0.006%, hot-rolling with a final rolling temperature FRT, to obtain a hot-rolled steel product having a thickness between 1.8 mm and 5 mm, then cooling down to a coiling temperature T.sub.coil satisfying: 450° C.≤T.sub.coil≤T.sub.coilmax with T.sub.coilmax=650−140×fγ, T.sub.coilmax being expressed in degrees Celsius and fγ designating the austenite fraction just before the coiling, and coiling to obtain a hot-rolled steel substrate, pickling and coating the hot-rolled steel substrate with Al or an Al alloy by continuous hot-dipping in a bath, to obtain a hot-rolled and coated steel sheet containing a hot-rolled steel sheet and an Al or an Al alloy coating, having a thickness between 10 and 33 μm, on each side of the hot-rolled steel sheet.

The hot-rolled coated steel sheet comprising: in wt %, C: 0.05-0.14%, Si: 0.1-1.0%, Mn: 1.0-2.0%, P: 0.001-0.05%, S: 0.001-0.01%, AI: 0.01-0.1%, Cr: 0.005-1.0%, Ti: 0.005-0.13%, Nb: 0.005-0.03%, N: 0.001-0.01%, Fe residues, and other inevitable impurities; a mixed structure of ferrite and bainite as a main phase; and as a remaining structure, one or more selected from the group consisting of martensite, austenite, and phase martensite (MA), wherein a fraction of the ferrite and bainite is 95-99 area % and Equation 1 is satisfied. [Equation 1] FCO.sub.{110}<112>+FCO.sub.{112}<111>≥10 where, FCO.sub.{110}<112> and FCO.sub.{112}<111>, each representing an area fraction occupied by a structure having ac crystal orientation of {110}<112> and {112}<111>.

The present invention provides steel sheet products having controlled compositions that are subjected to two-step annealing processes to produce sheet products having desirable microstructures and favorable mechanical properties such as high strength and ultra-high formability. Steels processed in accordance with the present invention exhibit combined ultimate tensile strength and total elongation (UTS.Math.TE) properties of greater than 25,000 MPa-%. Steels with these properties fall into the category of Generation 3 advanced high strength steels, and are highly desired by various industries including automobile manufacturers.