Bonded structure of dissimilar metallic materials and method of joining dissimilar metallic materials

Abstract

Disclosed herein are bonded structures and methods of forming the same. One embodiment of a bonded structure comprises first and second metallic layers and a bonding interface between the first and second metallic layers formed by diffusion and comprising a layer of at least one intermetallic compound. The intermetallic compound layer is formed in an area 52% or greater of an area of the bonding interface and has a thickness of 0.5 to 3.2 μm.

1 . A bonded structure of dissimilar materials made from metals comprising:
 a first metallic sheet;   a second metallic sheet overlying the first metallic sheet; and   a bonding interface between the first and second metallic sheets formed by diffusion and comprising at least one intermetallic compound layer, wherein the intermetallic compound layer is formed in an area 52% or greater of an area of the bonding interface and has a thickness of 0.5 to 3.2 μm.   
     
     
         2 . The bonded structure according to  claim 1  wherein the intermetallic compound layer is formed in an area 70% or greater of the area of the bonding interface. 
     
     
         3 . The bonded structure according to  claim 1  wherein the intermetallic compound layer has a thickness of 0.6 to 2.8 μm. 
     
     
         4 . The bonded structure according to  claim 1  wherein the intermetallic compound layer has a thickness of 0.8 to 2.5 μm. 
     
     
         5 . The bonded structure according to  claim 1  wherein the intermetallic compound layer is comprised of a crystal grain with a longitudinal diameter of 1.0 μm or less. 
     
     
         6 . The bonded structure according to  claim 1  wherein one of the first metallic sheet and the second metallic sheet comprises an iron-based alloy and the other comprises an aluminum-based alloy. 
     
     
         7 . The bonded structure according to  claim 6  wherein the intermetallic compound comprises an Fe—Al based compound. 
     
     
         8 . A method of bonding dissimilar materials made from metals comprising:
 overlying a first metallic sheet with a first melting point and a second metallic sheet with a second melting point to form a bonding interface, wherein the first melting point is lower than the second melting point;   rapidly heating the first and second metallic sheets;   rapidly cooling the first and second metallic sheets; and   forming a compound layer by diffusion comprising at least one intermetallic compound at the bonding interface by heat treating the first and second metallic sheets at a heat treatment temperature equal to or greater than a temperature at which dislocation loops and voids formed by atomic vacancies resulting from the rapid cooling are at least partially eliminated by a main component metal of the first metallic sheet.   
     
     
         9 . The method of  claim 8  wherein the heat treatment temperature is equal to or lower than ½ of a melting point in absolute temperature of the at least one intermetallic compound whose melting point is lowest among the at least one intermetallic compounds. 
     
     
         10 . The method of  claim 8  wherein the heat treatment temperature is equal to or higher than ½ of a melting point in absolute temperature of a main component metal of the first metallic sheet. 
     
     
         11 . The method of  claim 8  wherein the heat treatment temperature is equal to or lower than one of: ½ of a melting point in absolute temperature of the at least one intermetallic compound whose melting point is lowest among the at least one intermetallic compounds, and a temperature at which the first metallic sheet is softened by disappearance of a precipitation strengthening phase or recrystallization. 
     
     
         12 . The method of  claim 8 , wherein the rapid heating and the subsequent rapid cooling occurs by electric resistance joining by energization heating. 
     
     
         13 . The method of  claim 8 , wherein the rapid heating and the subsequent rapid cooling occurs simultaneously with baking in a painting process. 
     
     
         14 . A method of increasing bond strength between a dissimilar metal of an iron-based alloy and a dissimilar metal of an aluminum-based alloy, the method comprising:
 heat treating the dissimilar metals bonded by rapid heating and rapid cooling, the heat treating occurring at a temperature ranging from 130° C. to 440° C., thereby forming a compound layer by diffusion at a bond interface containing at least one Fe-Al based intermetallic compound.   
     
     
         15 . The method of  claim 14  wherein heat treating occurs at a temperature equal to or higher than 190° C. 
     
     
         16 . The method of  claim 14  wherein heat treating occurs at a temperature equal to or lower than 410° C. 
     
     
         17 . The method of  claim 14  wherein the iron-based alloy is a zinc-plated steel sheet and wherein, prior to heat treating, the method further comprises:
 eutecticly fusing zinc of the zinc-plated steel sheet and aluminum of the aluminum-based alloy, thereby forming a low melting point fused material; 
 removing an oxide coating on a surface of the aluminum-based alloy at the bonded interface together with the fused material; and 
 bonding by rapid heating and rapid cooling new surfaces of both dissimilar metals from which a zinc-plating layer and the oxide coating are removed. 
 
     
     
         18 . The method of  claim 17  wherein the rapid heating and the subsequent rapid cooling occurs by electric resistance joining by energization heating. 
     
     
         19 . The method of  claim 17  wherein the rapid heating and the subsequent rapid cooling occurs simultaneously with baking in a painting process.