Influence of Filler Alloy Composition and Process Parameters on the Intermetallic Layer Thickness in Single-Sided Cold M
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DUCING the vehicle weight to improve fuel efficiency and simultaneously increasing the passenger’s safety are unbroken trends in the modern automotive industry. Particularly high-strength steels, e.g., dual phase (DP), transformation-induced plasticity (TRIP), and twinning-induced plasticity (TWIP) steel grades[1,2] as well as aluminum (Al) alloys, e.g., series AW 5xxx and AW 6xxx,[3–5] play important roles in innovative multimaterial car body design. In order to benefit from
ZAHRA SILVAYEH, RUDOLF VALLANT, and CHRISTOF SOMMITSCH are with the Graz University of Technology, Institute of Materials Science, Joining and Forming (IMAT), Kopernikusgasse 24/I, 8010 Graz, Austria. Contact e-mail: [email protected] BRUNO GO¨TZINGER and WERNER KARNER are with the Magna Steyr Engineering Austria AG & Co KG and Magna Steyr Fahrzeugtechnik AG & Co KG, Liebenauer Hauptstraße 317, 8041 Graz, Austria. MATTHIAS HARTMANN is with the Austrian Institute of Technology (AIT), Light Metals Technologies Ranshofen GmbH (LKR), P.O. Box 26, 5282 Ranshofen, Austria. Manuscript submitted January 13, 2017.
METALLURGICAL AND MATERIALS TRANSACTIONS A
the specific advantages of each of these material groups and to obtain car bodies offering both high safety and low weight, joining of aluminum alloys with steels is mandatory.[6] Various processes for mechanical joining, adhesive bonding, brazing, and welding of dissimilar metal sheets in the automotive industry were developed.[6–8] Basically, two main welding process categories are distinguished: solid-state welding and fusion welding, both including various subcategories.[9–11] An opportunity for joining particularly thin metal sheets by combining the advantages of both fusion and solid-state welding offers the Cold Metal Transfer (CMT) process developed by Fronius.[12] The CMT process enables spatter-free joining of similar metals, e.g., Al-Al bead-on-plate[13–15] or butt welding,[16] as well as joining of dissimilar metals, e.g., Al-steel butt welding with tapered steel sheet edges,[17–19] overlap welding,[20–29] or even spot welding.[30–32] In comparison with conventional gas metal arc (GMA) welding processes, the heat input of the CMT process is significantly reduced. Since both the aluminum-based sheet and the filler melt whereas the steel sheet remains solid, joining is achieved by the combination of aluminum welding and steel brazing.[17–21]
max. 2.0 bal. bal. bal. bal. bal. 0.55-0.6 bal. 0.3-0.5 0.4-0.6 bal. 0.2-0.3 0.3-0.5 bal. Cr+Mo 10 lm
Fig. 9—Merged optical micrograph of the joint cross section of sample 08 (a). The details (b) through (e) show sections of a long crack which is initiated at the surface at the base corner of the weld (b) and which runs transversely through the IM layer toward the cutting edge of the steel sheet (e).
were formed when the Robacta500 torch was utilized for welding (samples 07 and 08). The influence of the torch type was even more pronounced when using filler Al-3Si-1Mn. As stated before, and as shown in Figure 8, IM layers of x < 4 lm and predominantly
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