ALAW2007

Laser Roll Welding of Dissimilar Metal Joint of Zinc Coated Steel and Aluminum Alloy

Hitoshi Ozaki and Muneharu Kutsuna Nagoya University, Japan

2007.4.19

Shigeyuki Nakagawa and Kenji Miyamoto Nissan Motor Co., Ltd., Japan

Contents 1. 1.Introduction Introduction 2. 2.What WhatisisLaser LaserRoll RollWelding? Welding? 3. 3.Laser LaserRoll RollWelding Weldingof ofGI GIsteel steelto toA6000 A6000Al Alalloy alloy 3.1 3.1Experimental Experimentalprocedure procedure 3.2 3.2Bead Beadappearance appearanceand andcross-section cross-sectionof ofLRW LRWwelds welds 3.3 3.3Effect Effectof oftravel travelspeed speedon oninterlayer interlayerof ofjoint joint 3.4 3.4Effect Effectof ofroll rollpressure pressureon oninterlayer interlayerof ofjoint joint 3.5 3.5Mechanical Mechanicalproperties propertiesof ofWelded Weldedjoint joint

4. 4.Conclusions Conclusions

1.1 Background ～Issues in automotive industry～ Low Lowfuel fuelconsumption consumption by bylightening lightening

Safety Safetyimprovement improvement

Concept of “hybrid body structure”

An Anexample exampleof of“hybrid “hybridbody bodystructure” structure” Use of high strength steel → Lightening with improving strength Use of aluminum alloy → Lightening

However… However… ItIt is is difficult difficult to to join join steel steel to to aluminum aluminum by by fusion fusion welding. welding.

1.2 Fusion welding of steel to aluminum Problems Problemsininfusion fusionwelding weldingof ofsteel steelto toaluminum aluminum Brittle intermetallic compounds (IMC's) are formed at weld interface.

Brittle IMC’s Ductile IMC’s M.Yasuyama, et al., 1996

Brittle IMC's should be minimized by application of Laser Roll Welding.

1.3 Objectives of this study 1)

Laser Roll Welding of zinc coated steel to aluminum alloy was investigated to make a reliable dissimilar joint. The following process parameters should be controlled.

Parameter Parameter tree treeof of LRW LRW

2)

The effects of the process parameters on the joinability, the formation of IMC layer and the mechanical properties of joints should be made clear.

Contents 1. 1.Introduction Introduction 2. 2.What WhatisisLaser LaserRoll RollWelding? Welding? 3. 3.Laser LaserRoll RollWelding Weldingof ofGI GIsteel steelto toA6000 A6000Al Alalloy alloy 3.1 3.1Experimental Experimentalprocedure procedure 3.2 3.2Bead Beadappearance appearanceand andcross-section cross-sectionof ofLRW LRWwelds welds 3.3 3.3Effect Effectof oftravel travelspeed speedon oninterlayer interlayerof ofjoint joint 3.4 3.4Effect Effectof ofroll rollpressure pressureon oninterlayer interlayerof ofjoint joint 3.5 3.5Mechanical Mechanicalproperties propertiesof ofWelded Weldedjoint joint

4. 4.Conclusions Conclusions

2.1 What is Laser Roll Welding? Laser LaserRoll RollWelding Weldingfacility facility

Laser Roll Welding was developed for joining of dissimilar metals by M.Kutsuna, M.Rathod and A.Tsuboi in 2002. A pressure roller was mounted on a 2.4 kW pulse CO2 laser facility. The thermal cycle for joining should be shortened by laser heating with a low heat input. Because, the formation of brittle IMC’s should be avoided. Furthermore, good contact of two metal sheets and rapid heat transfer from a upper sheet to a lower sheet are conducted in one time by this pressure roller.

2.2 Characterization of Laser Roll Welding Classification Classificationof ofwelding weldingprocesses processes

4. Laser Roll Welding

1. Fusion welding Joint by melting and alloying a part of both base metal.

2. Solid-state welding Joint by the use of interdiffusion and the plastic flow phenomenon in the interface.

3. Brazing Joint that uses brazing filler metal of low melting point for faying surface.

By heating only metal A and pressurizing the both metals, the heat is conducted to metal B. Molten phase is formed at the faying surface and joining is finished by cooling.

ItItisisnot notpertinent pertinentto toany anyamong amongleft left three welding processes. three welding processes. ItItshould shouldbe beclassified classifiedas asthe thefourth fourth welding weldingcategory. category.

2.3 Joining mechanisms of Laser Roll Welding Type TypeⅠⅠ Combination of metals with large difference in their melting points.

ex) Fe

– Al

Only the metal of a high melting point is heated up to elevated temperature for avoid brittle IMC’s. The interlayer is formed and cooled rapidly to minimize the thickness.

Type TypeⅡⅡ Combination of metals with eutectic reaction at lower temperature.

ex) Ti

– Fe

The eutectic reaction occurs at a lower temperature than those of both metals. The interlayer of the eutectic phase is formed.

Contents 1. 1.Introduction Introduction 2. 2.What WhatisisLaser LaserRoll RollWelding? Welding? 3. 3.Laser LaserRoll RollWelding Weldingof ofGI GIsteel steelto toA6000 A6000Al Alalloy alloy 3.1 3.1Experimental Experimentalprocedure procedure 3.2 3.2Bead Beadappearance appearanceand andcross-section cross-sectionof ofLRW LRWwelds welds 3.3 3.3Effect Effectof oftravel travelspeed speedon oninterlayer interlayerof ofjoint joint 3.4 3.4Effect Effectof ofroll rollpressure pressureon oninterlayer interlayerof ofjoint joint 3.5 3.5Mechanical Mechanicalproperties propertiesof ofWelded Weldedjoint joint

4. 4.Conclusions Conclusions

3.1.1 Materials Zinc coated steel

Dimension : 125×180×0.55 mm

◇ GI type of galvanized steel sheet (= GI) Table 1 Chemical compositions and coating weight of steel sheet Material GI

Elements (mass%) C

Mn

P

S

Coating weight （g / m2）