was seen in two morphologies (Fig. 15), one with a MgSiSr core (Fig. 15C) and one without (Fig. 15D). Dendritic Si was seen in grain boundaries, and AlMnFeSi phase (Al19Fe4Mn1Si2) within the Si dendritic region was observed as well. The TEM results for the Aural-2- T7 to AA6022-T4 weld nuggets are shown in Fig. 16. These weld nuggets are composed almost entirely of material from the Aural-2-T7 substrate — Fig. 5. Figure 16 also reveals primary aluminum surrounded by a more complex aluminum-silicon eutectic structure. The needle-like phase -Al5FeSi was seen in the eutectic region — Fig. 16C. In summary, further strengthening in the Aural-2-T7 to AA5754-O and Aural-2-T7 to AA6022-T4 spot weld nugget as shown in Figs. 9 and 10 are the direct result of the formation of various forms of intermetallic particles within the Al-Si eutectic regions surrounding primary aluminum. Conclusions Three types of spot welds between dissimilar aluminum alloys, namely, Aural-2-T7 to Aural-2-T7, Aural 2-T7 to AA5754- Fig. 11 — FIB images of spot welds obtained from FIB. A — Aural2T7 for welding schedule 1; B — Aural2/ T7 to AA5754; C — Aural2T7 in each image guide the boundaries of the weld nugget and Aural2T7. A B to Aural2T7 O, and Aural-2-T7 to AA6022-T4, were successfully produced using General Motors’s proprietary MRD resistance spot welding process. The constitutive behavior of these three resistance spot weld nuggets as well as that of the HAZ for the Aural-2-T7 and AA6022-T4 side were determined using modified shear testing coupled with digital image correlation. This local-scale data of the specific weld nugget and HAZ properties can be to AA6022T4. Red dash lines used as input to multiscale modeling of macroscale joints, an example of which shall be published in a separate body of work. All the weld nuggets were found to have higher yield strength than the base Aural-2-T7 material. This was found to be a result of grain refinement that occurs during the resistance spot welding process and would be typical for any combination of Al WELDING RESEARCH 254-s WELDING JOURNAL / JULY 2016, VOL. 95 Fig. 12 — A — STEM HAADF and corresponding EDS combination map; B — corresponding EDS elemental maps of Aural2T7 . A C B
Welding Journal | July 2016
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