A method to treat the magnesium surface to manufacture the metallic assembly with the polymer and magnesium to have excellent bonding strength is disclosed.

As a method to treat the magnesium surface for the bonded coupling of the mixture of the polymer and magnesium, this is a method including, (a) an etching step, wherein the magnesium surface is treated with an acidic solution; (b) a first surface treatment step, wherein the magnesium surface is treated with ultrasonic waves; (c) a second surface treatment step, wherein the magnesium surface is treated with an acidic solution; (d) a first silane coupling processing step, wherein the magnesium surface is treated with ultrasonic waves; (e) a surface activation treatment step, wherein the magnesium surface is treated with acidic solution; and (f) a second silane coupling processing step, wherein the magnesium surface is treated with ultrasonic waves.

A magnesium alloy/resin composite structure (106) including a magnesium alloy member (103) and a resin member (105) integrated to the magnesium alloy member (103) and made of a thermoplastic resin composition, in which the magnesium alloy member (103) surface to which the resin member (105) is not integrated is coated with a layer including a manganese atom, an oxygen atom, and a sulfur atom.

A magnesium alloy/resin composite structure (106) including a magnesium alloy member (103) and a resin member (105) integrated to the magnesium alloy member (103) and made of a thermoplastic resin composition, in which the magnesium alloy member (103) surface to which the resin member (105) is not integrated is coated with a layer including a manganese atom, an oxygen atom, and a sulfur atom.

A magnesium alloy part is inserted into a mold, a resin composition is injected and joined to the part, and a composite is obtained. A part having, formed thereon, a surface layer of a metal oxide, a metal carbonate, or a metal phosphate in use of a usual conversion treatment or a modification method thereof can be used for the magnesium alloy plate 1. The surface that has a larger amount of crystal-like objects of a nanolevel on the surface layer composed of the metal oxide, metal carbonate, or metal phosphate has a higher level of hardness, microscopic roughness, and good injection joining force, and these parameters can be controlled by a conversion treatment method. A resin composition 4, containing PBT or PPS as the main component, is used as the resin composition part.

A magnesium alloy part is inserted into a mold, a resin composition is injected and joined to the part, and a composite is obtained. A part having, formed thereon, a surface layer of a metal oxide, a metal carbonate, or a metal phosphate in use of a usual conversion treatment or a modification method thereof can be used for the magnesium alloy plate 1. The surface that has a larger amount of crystal-like objects of a nanolevel on the surface layer composed of the metal oxide, metal carbonate, or metal phosphate has a higher level of hardness, microscopic roughness, and good injection joining force, and these parameters can be controlled by a conversion treatment method. A resin composition 4, containing PBT or PPS as the main component, is used as the resin composition part.

Composition, characterized in that: —it comprises, in a solution of demineralized water: between 10 and 80, preferably between 15 and 20, more preferably 17, g/l of a composition of phosphoric acid H.sub.3PO.sub.4, and between 2 and 15, preferably between 4 and 8, more preferably 6, g/l of a composition of potassium permanganate KMnO.sub.4, —the weight ratio H.sub.3PO.sub.4/KMnO.sub.4 is between 1.5 and 10, preferably between 1.8 and 5, mote preferably equal to 2.8, —said composition has a pH between 2.4 and 3, preferably 2.5.

Composition, characterized in that: —it comprises, in a solution of demineralized water: between 10 and 80, preferably between 15 and 20, more preferably 17, g/l of a composition of phosphoric acid H.sub.3PO.sub.4, and between 2 and 15, preferably between 4 and 8, more preferably 6, g/l of a composition of potassium permanganate KMnO.sub.4, —the weight ratio H.sub.3PO.sub.4/KMnO.sub.4 is between 1.5 and 10, preferably between 1.8 and 5, mote preferably equal to 2.8, —said composition has a pH between 2.4 and 3, preferably 2.5.

The etching agent is an aqueous solution including at least one acid selected from the group consisting of inorganic acids other than nitric acid, and organic acids; and an organic nitrogen compound having a molecular structure containing N—OH or N—O.sup.−. The acid concentration of the etching agent is 0.05 to 3% by weight, and the organic nitrogen compound concentration of the etching agent is 0.005 to 5% by weight. By bringing the etching agent into contact with a surface of a magnesium component, fine irregularities can be formed on the surface of the magnesium component even when etching depth is large.

The etching agent is an aqueous solution including at least one acid selected from the group consisting of inorganic acids other than nitric acid, and organic acids; and an organic nitrogen compound having a molecular structure containing N—OH or N—O.sup.−. The acid concentration of the etching agent is 0.05 to 3% by weight, and the organic nitrogen compound concentration of the etching agent is 0.005 to 5% by weight. By bringing the etching agent into contact with a surface of a magnesium component, fine irregularities can be formed on the surface of the magnesium component even when etching depth is large.

Provided is an alloy member including a substrate made of magnesium-lithium alloy with a sum of content of magnesium and content of lithium of 90 mass % or more and a coating film disposed on the substrate. The coating film contains fluorine and oxygen, with a fluorine content of more than 50 atom % and an oxygen content of less than 5 atom %.