Corrosion Behavior of Friction Stir Welded Hpdc AM60B Lap Joints
Bibliographic record
Abstract
Capitalizing on the potential for Mg alloys to reduce vehicle weight, a multi-national Mg-intensive front end research and development (MFERD) initiative has been established to identify and address the processing, joining and corrosion protection challenges that need to be overcome to support the fabrication of a complete Mg-intensive automotive front end assembly. The initiative identified high pressure die-cast (HPDC) AM60B and linear friction stir welding (FSW) as the preferred structural casting and joining technology, respectively, to be used for the fabrication of demonstrator sub-assemblies for component-level testing. A key fundamental aspect underpinning the successful implementation friction stir welded HPDC AM60B joints is a well-developed understanding of the extent of atmospheric corrosion damage expected to occur across the joint when boldly-exposed. The susceptibility of HPDC AM60B to localized corrosion arises from the heterogeneous microstructure and the formation of galvanic couples between the Mg matrix and the secondary intermetallic phases. Friction stir welding has been reported to significantly alter this heterogeneous microstructure across the welded joint. However definitive links between microstructure and localized corrosion susceptibility remain elusive. Electrochemical polarization and scanning vibrating probe (SVP) measurements were made to establish links between the localized corrosion susceptibility observed across the FSW joint and the resultant variations in microstructure, as revealed by scanning electron microscopy (SEM). Microstructural parameters of interest included microhardness, grain size and the size and spacial distribution of Al-Mn intermetallic particles and the secondary Mg 17 Al 12 (β) phase. The corrosive environment used was a near-neutral 5 wt.% NaCl solution. Complementary surface analyses by X-ray photoelectron spectroscopy (XPS) of the starting surface films were made to delineate the role played by the native oxide film on the subsequent localized corrosion susceptibility. The findings based on the bulk immersion testing were subsequently validated by continuous salt fog atmospheric corrosion testing. Of the microstructural parameters studied, only the grain size and spacial distribution of the secondary Mg 17 Al 12 (β) phase were significantly affected across the friction stir welded joint. The stir zone exhibited a finer grain size relative to the unaffected base material, but did not exhibit a secondary Mg 17 Al 12 (β) phase network. The combined set of electrochemical measurements (open-circuit potential, potentiodynamic polarization and SVP) consistently revealed that the stir zone was more susceptible to localized corrosion than the unaffected base material. SVP measurements on both the original topography and a flat-polished surface demonstrated that the stir zone striations had little effect on this tendency (see Figure 1). The findings thus far point to a combined alloy chemistry and structure link (centering on the fate of the secondary Mg 17 Al 12 (β) phase network) between the localized corrosion susceptibility observed across the friction stir welded joint and the resultant variations in microstructure. Figure 1
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How this classification was reachedexpand
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 | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| 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 itClassification
machine, unvalidatedMachine predicted; a candidate call from one teacher head, not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".