The Effects of Aging on the Microstructure and Mechanical Properties of Bi-Containing Sn-Rich Alloys
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Bibliographic record
Abstract
ABSTRACT A significant reliability concern with lead-free solder alloys such as SAC 305 is the degradation of mechanical properties after aging at both elevated and room temperature, due to the coarsening and recrystallization of the microstructure. It has been shown in earlier studies that the inclusion of bismuth (Bi) in these alloys leads to a stabilization of the microstructure and subsequent maintenance of as-cast properties after aging. The goal of this paper and ongoing research is twofold – to ascertain whether these trends hold at a large range of aging temperatures and times, and to understand the underlying metallurgical mechanisms that lead to these effects. This paper examines the effects of aging on the microstructure and hardness of Bi-containing Sn-rich alloys. The alloys studied were Sn-1Bi, Sn-5Bi, Sn-0.7Cu-1Bi, and Sn-0.7Cu-5Bi, as well as a baseline alloy, SAC 305. These alloys were aged both at room temperature (between 10 and 365 days) and at elevated temperature (100°C and 125°C, between 1 and 14 days). As-cast microstructure and properties were also included. Cooling after elevated temperature aging was performed in air. The microstructure was evaluated using Scanning Electron Microscopy, and hardness was measured using a Rockwell hardness tester HR15X with a ¼” carbide ball indenter. For Bi-containing alloys, bismuth precipitates became more uniformly distributed as aging proceeded, and hardness did not undergo any appreciable changes. SAC 305, on the other hand, showed a predictable decay in hardness after all aging treatments.
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Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.001 | 0.002 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.002 | 0.001 |
| Research integrity | 0.001 | 0.002 |
| Insufficient payload (model declined to judge) | 0.000 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from it