Post weld heat treated AA6061-T6 alloy resulted from the application of a Cu donor stir assisted (CDSA) friction stir welding (FSW) material was examined for crystal structure and mechanical properties. CDSA FSW samples were tested at a constant tool rotational speed of 1400 rpm and a welding translational speed of 1 mm/s. CDSA samples of 20% and 60% thickness of the AA6061-T6 base alloy were selected to assist the FSW joining at the plunge stage. The FSW AA6061-T6 samples were solid solution treated at 540 °C for one hour, followed by quenching in water at room temperature. The samples were then artificially aged at 180 °C for 6 hours, respectively, followed by air cooling. The samples were tested for microstructure, crystal structure, chemical composition, and mechanical properties using optical microscopy, scanning electron microscopy, X-ray diffraction, and nanoindentation. The microstructure shows the additional grain refinement in the stir zone (SZ) due to recovery and recrystallization with increasing aging time. Examination of the chemical contents of the FSW AA6061-T6 alloy samples using scanning electron microscopy with energy dispersive spectroscopy (EDS) revealed Al (parent material) as the predominant element, while Cu (CDSA) was minimally present as expected. XRD results of the CDSA FSW samples depicted crystal orientations similar to the orientations of the AA6061-T6 alloy. Nanoindentation tests revealed softening effects due to the dissolution of hardening precipitates at the SZ. The hardness of the base metal (BM), left and right regions, is reported as ~ 6.5 GPa, whereas at the SZ, the hardness is ~ 5.5 GPa at a depth of indentation of 4.7 µm.

Electronic packaging industries are in an ongoing transition to lead free soldering due to the adverse effect on environment and human health [1]. Sn-Ag-Cu (SAC) have been recognized as promising alternatives due to its low eutectic temperature, higher wettability and strength, superior resistance to creep and thermal fatigue. Surface roughness has a significant influence on mechanical parameters determined nanoindentation tests. Although research has been conducted to analyze the mechanical properties of bulk SAC material, there have been limited prior studies on SAC thin films and their mechanical properties since fabricating a smooth SAC thin film is a fundamental challenge. SAC thin films with four different Sn–Ag–Cu ternary eutectic composition: 96.5Sn-3.0Ag-0.5Cu, 95.5Sn-3.8Ag–0.7Cu, 95.5Sn-3.9Ag–0.6Cu & Sn-4.0Ag–0.5Cu will be deposited using RF magnetron sputtering with different deposition rates and annealed at various temperature to fabricate a smooth continuous film. Figures 1 and 2 depict SAC05 deposited using RF magnetron sputtering at Figure 1: SEM image of SAC-05 surface at 10,000X. 20W, 2.4 mTorr pressure, and argon flow flow rate of 20.5 sccm. Surface morphology will be examined using Field emission Scanning electron microscopy (FE-SEM) and atomic force microscopy (AFM). Crystallinity of the deposited film will be examined using X-ray diffraction (XRD). Mechanical properties will be studied using nanoindentation [2]. Properties of the thin film will be compared with the bulk material with similar eutectic composition. References M. Abtew G. Selvaduray. (2000). Lead-free Solders in Microelectronics. Materials Science & Engineering. a Review Journal., 27(5-6), 95. Long, X., Wang, S., Feng, Y., Yao, Y., & Keer, L. M. (2017). Annealing Effect on Residual Stress of Sn-3.0Ag-0.5Cu Solder Measured by Nanoindentation and Constitutive Experiments. Materials Science and Engineering: A, 696, 90-95. Figure 1

Friction stir welding of high-strength materials such as steels is the impeded by the lack of the vast heat input needed to start the process. Contact friction is considered the most dominant source of heat generation for FSW steels which tends to cause severe wear conditions of the tool hear. To relieve the extreme wear conditions that occur on the tool heads because of FSW steels, we introduce the non-mixing Cu donor stir material to friction stir welding of aluminum alloys. The elastic properties of the Cu donor assisted friction stir welded aluminum alloys are measured using nanoindentation. The hardness and elastic modulus were measured for two regions, the base metal (BM) and the stir zone (SZ). The measurements were conducted for 20% and 60% Cu non-heat treated (NHT) and heat-treated (HT) samples. The nanomechanical properties were measured using nanoindentation with the continuous stiffness method (CSM) in depth control. The HT samples are softer than the NHT samples as expected. However, the 20% Cu NHT and HT samples depicted the same hardness at the SZ. Similar results were observed for the 60% Cu donor stir samples. It therefore concluded that the SZ is softer than the BM for the 20% and 60% Cu donor stir material as expected. The hardness of the weld at the SZ is similar to the hardness of the Al6061-T6 plate, suggesting that the Cu donor stir material did not impact the hardness properties of the Al6061-T6 plate due to the depletion of the Cu donor stir material during the welding process, an important result of the concept of the donor material. The elastic moduli of the Cu donor stir welded samples vary between 75~85 GPa at a depth of indentation of ~4600 nm, which are different from the elastic moduli of Cu 110 (117.2 GPa) and similar to the elastic modulus of aluminum alloys (68.9 GPa), an important outcome.

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