13th International Conference on Aluminum Alloys (ICAA13): Forming and Joining 4
Program Organizers: William Cassada, Alcoa Technical Center; Hasso Weiland, Alcoa Technical Center; Anthony Rollett, Carnegie Mellon University

Tuesday 2:00 PM
June 5, 2012
Room: Rangos II
Location: University Student Center

Session Chair: Shi-Hoon Choi, Sunchon National University

2:00 PM  
Fatigue and Creep Properties of Al-Si Brazing Filler Metals: Masakazu Edo1; Masatoshi Enomoto2; Yoshimasa Takayama3; 1Mitsubishi Aluminum Co.Ltd; 2Japan Light Metal Welding Association; 3Utsunomiya University
     The manufacturing process for automotive heat exchangers involves brazing using an aluminum brazing sheet. To ensure structural strength and improve durability, it is necessary to acquire mechanical properties for each of the materials. Al-Si alloys are most commonly used as the filler metal; however, the properties of the fillets formed by the solidification of the Al–Si filler melt have scarcely been reported previously. In this study, fatigue and creep properties of Al–10mass%Si cast alloy, which is considered to have the same chemical composition and metallic structure as those of the filler metal after brazing, were investigated. From the measured results of samples at various cooling rates during solidification, it was found the eutectic silicon particle size of the Al–Si alloy strongly related to these properties. These results showed that the finer silicon particles improved the fatigue and creep properties of fillets, even those with the same composition.

2:20 PM  
Effect of Additional Elements of Al-Si Filler Alloy on Flowability and Clearance Fillability during Brazing: Masakazu Edo1; Michihide Yoshino1; Shuu Kuroda1; 1Mitsubishi Aluminum Co.Ltd
    Aluminum alloys are widely used for automotive heat exchangers manufactured by brazing processes. All joint gaps must be filled with Al-Si filler metal to prevent the leak of refrigerant. Recently, brazing of heat exchanger components has become difficult due to the decrease in the thickness of the brazing sheets. Since the fluidity of Al-Si molten metal is very high, the flow of molten filler metal sometimes causes dissolution of the base metal or defect of joints. In this study, we investigated the effect of additional elements (such as Mn, Fe, Ti and Zr) of Al-Si filler metal on the flowability and clearance fillability using our original evaluation model. The results indicated that the addition of Mn or Ti improved the clearance fillability significantly. We clarified the mechanism that additional elements change the properties of molten filler metal, by measuring the viscosity of each filler metal and observing the solidified microstructure.

2:40 PM  
Influence of Erosion Phenomenon on Flow Behavior of Liquid Al-Si Filler Between Brazed Components: Takahiro Izumi1; Toshiki Ueda1; 1Kobe Steel, Ltd.
    Automotive heat exchangers are predominantly composed of plates, tubes and fins. Each component is brazed by using Al-Si filler. In the plate/tube/fin brazed-structures, the flow of the liquid filler between the components affects the fillet size at each joint. In this study, the influence of the erosion phenomenon, i.e., silicon diffusion from the braze cladding into the core alloy, in the tube on the flow behavior of the liquid filler flowing on the tube from the plate to the fin has been investigated. As a result, the area of the liquid filler not flowing but existing around α phases on the tube during brazing, which is defined as filler flow channel, can change depending on the erosion degree. The flow ability of the liquid filler flowing from the plate to the fin increases as the area increases.

3:00 PM Break

3:30 PM  
Effects of Plate Thickness and Projection Shape on the Microstructure and Strength of High-Speed Solid-State Joined 2024 Alloy Studs and 5052 Alloy Plates: Shinji Kumai1; Keisuke Hayashida1; Kento Takaya1; 1Tokyo Institute of Technology
    An advanced stud joining method was developed that produces a strong joint without mechanical property degradation of the base materials. Specially designed 2024-T3 aluminum alloy studs with a circular ridge projection were pressed against 5052-H34 aluminum alloy plates of 1 to 4 mm in thickness. A high-density discharge current was run through the stud, and flowed through the projection and plate surface for several milliseconds, prompting local heating, plastic deformation, and atomic diffusion at the contact point. The projection crushed and spread along the plate surface. Asymmetrical deformation occurred on both the inner side and the outer side of the projection. For thin plates, joining mainly occurred at the outer side. For thick plates, in contrast, the deformation was largely symmetrical. Effects of discharge voltage and the projection shape were also investigated in an attempt to optimize joining strength.

4:10 PM  
Joining of 2024 Aluminum Alloy Stud to AZ80 Magnesium Alloy Extruded Plate by Advanced High-Speed Solid-State Method: Yohei Harada1; Yutaro Sada1; Shinji Kumai1; 1Tokyo Institute of Technology
    For its potential usefulness for weight reduction, an advanced high-speed solid-state joining method was tested for its applicability to the joining of 2024 aluminum alloy studs to AZ80 magnesium alloy extruded plates. In this method, a stud having a circular projection at its bottom is pressed against a plate surface, whereupon a discharge current applied to the upper part of the stud flows through a contact point between the projection and the plate to form a joint between them. Observations of the joint area reveal a projection structure sticking into the plate and bending toward the outside, in line with the predominant path of current flow. Refined grains of AZ80 magnesium alloy were observed in the vicinity of the joint interface. This reveals that local plastic deformation and heating induced dynamic recrystallization within the plate. Tensile fracture strength was not found to increase with increasing discharge voltage. To maximize that strength, it was instead found necessary to select an appropriate discharge voltage.

3:50 PM  
Interfacial Reaction during Dissimilar Joining of Aluminum Alloy to Magnesium and Titanium Alloys: Joseph Robson1; Chaoqun Zhang1; Alexandra Panteli1; Dolhats Baptiste2; Emma Cai3; Philip Prangnell1; 1University of Manchester; 2Université de Nantes; 3Altrincham Girls' Grammar School
    Ultrasonic welding, a solid state joining process, has been used to produce welds between AA6111 aluminum alloy, cast and wrought magnesium alloys, and titanium 6Al-4V alloy. The mechanical properties of the welds have been assessed and it has been shown that it is the nature and thickness of the intermetallic compounds (IMCs) at the joint line that is critical in determining the strength and fracture energy. In particular, it is demonstrated that the IMC that forms in Al-Ti alloy welds is less detrimental to properties than the thick IMC layer formed in the Al-Mg welds. A model has been developed to predict IMC formation during welding and provide an understanding of the critical factors that determine the IMC layer thickness in welds between aluminum and dissimilar metals. This has been used identify strategies for controlling the IMC layer thickness and hence weld properties.

4:30 PM  
Interface Structure and Bonding in Rapid Dissimilar FSSW of Al to Steel Automotive Sheet: Phil Prangnell1; Yingchun Chen1; 1The University of Manchester
    Producing robust joints between Al and steel sheet by friction stir spot welding (FSSW), within a weld cycle time short enough for industrial application, is extremely challenging. The issues faced by conventional FSSW are discussed, including the role of the material flow behaviour and modelling of the intermetallic reaction layer seen at the weld interface. A possible solution is presented, termed “Abrasion Circle Friction Spot Welding”; with this approach a probe tool is translated through a circular path to abrade the steel surface. It is shown that successful welds can be produced between Al-61111 and DC04 steel 1 mm sheets with a cycle time <1 second that exhibit high failure loads and a nugget pullout fracture mode. The mechanisms of weld formation and the joint interface structure are discussed. TEM investigation of the joint interface revealed no intermetallic reaction layer with this process.

4:50 PM  Cancelled
Simultaneous Behavior of Foaming and Bonding for Aluminum Foam Panel: Yuko Okano1; Yuji Kume1; Makoto Kobashi1; Naoyuki Kanetake1; 1Nagoya University
    Sandwich panels consisting of an aluminum foam core and Al alloy face sheets have outstanding features such as high specific stiffness and high energy absorption. In this work, the possibility of the simultaneous processing of foaming of precursor and bonding with Al sheet was investigated in order to simplify manufacturing process of the sandwich foam panels without pre-bonding or post-bonding. A precursor of Al-7%Si alloy with 0.5wt.% TiH2 was putted on the pure Al sheet and heated between two graphite dies with various spaces. After heating to various temperatures, they were rapidly cooled. Foaming behavior of the precursor was observed in the cross section of the specimen and bonding behavior with the pure Al sheet was evaluated by the bonding area with the peel test. Bonding area was varied depending on the die space and heating temperature, and the favorable temperature for homogeneous foaming was not sufficient for well bonding.