An accumulative roll-bonding (ARB) method is one of severe plastic deformation methods that improve a mechanical characteristic by ultra-micronizing a crystalline grain level of a metallic material up to a submicron range.
In general, in order to manufacture a copper alloy sheet having high strength and electrical conductivity, the copper alloy sheet has been manufactured by rolling a copper alloy manufactured by adding an alloy element to increase the strength by rolling, and the like.
However, when a content of the alloy is increased in order to improve the strength, electrical conductivity and rollability deteriorates, as a result, there is a limit in acquiring both high strength and high electrical conductivity.
In other words, in existing plastic deformation methods such as rolling or extruding, when a processing amount is increased, a shape (cross sectional area) of a target material is inevitably changed, and as a result, there may be a limit in accumulating deformation energy in a material. Therefore, existing plastic deformation methods cannot actually show a large effect in crystalline grain micronization and high strength of a metallic material.
As a result, a method of increasing the strength by micronizing a crystalline grain to a hundred-nanometer size by performing consecutive rolling processing by using the accumulative roll-bonding method is used.
In other words, the accumulative roll-bonding method has been applied on steel and aluminum (Al) materials which are representative as structural materials but does not larger advantages than existing reinforcing methods such as a high solution reinforcing method, a deposition reinforcing method, and the like only by achieving high strength in terms of commercialization.
Therefore, in order to advance the commercialization by maximally showing a characteristic of the existing accumulative roll-bonding (ARB) method, a lot of research and development are in progress with respect to an accumulative roll-bonding method for achieving crystalline grain micronization and high strength.
For example, Korea Patent Unexamined Publication No. 2006-0013211 discloses a manufacturing method of high-strength CU workpiece by using an accumulative roll-bonding process.
In brief, copper sheets having a predetermined length, which are surface-treated are overlapped and fixed and thereafter, rolled and bonded and the bonded copper sheets are cut, but such a process is repeated several times to manufacture copper sheets that are overlapped in multiple layers.
However, there is a limit in increasing a pure copper alloy sheet by crystalline grain micronization.
Further, when the existing high-strength copper alloy sheets accumulated and roll-bonded in order to increase the strength, a plurality of cracks occur in the roll-bonding and the sheets are not bonded, and as a result, it is impossible to manufacture a quality sheet.
Moreover, a problem is caused in which electrical conductivity is significantly decreased when the high-strength copper alloy sheet is used.
Japanese Patent Unexamined Publication No. 2001-184788 discloses alumina distributed reinforced copper manufactured by roll-bonding with alumina grains applied and inserted between oxygen free copper sheets.
However, the publication has a problem in which when the alumina grains are applied between the oxygen free copper sheets and thereafter, rolled, uniform application of alumina is impossible.