Eutectic solidification of aluminum-silicon alloys

Abstract

Surface 3 of alloy AA6111-T4, even deeper into the weld material, showed similar results.Finally, we note that we did not perform a complete investigation of the base metal. However, some preliminary results indicate that the 6111 base metal had a much stronger texture than the 5182. This difference could be another reason why the 6111 material had a stronger texture in the columnar grain region of the weld.From these results, we can conclude that a strong cube texture forms in laser-welded AA5182-O and AA6111-T4 alloys and that the strength of the texture depends on the particular alloy and the depth through the weld zone. In particular, we note that the columnar grains that form on either side of the weld centerlines and appear to grow out from the parent metal into the liquid are highly textured, with a Ͻ001Ͼ direction parallel to the growth direction. This result is in agreement with studies of solidification in aluminum alloys that reported that a cube direction is a preferred growth direction. [15] Given that mechanical properties are strongly dependent on texture, [16] one would expect this texture could have a strong effect on the local mechanical response of the welds.The authors thank R. Mishra, for his critical review of the manuscript, and J. Cross, for his assistance in metallographic sample preparation and microhardness measurements. It is a pleasure to acknowledge stimulating discussions with P. Krajewski and M. Verbrugge. The work at Brown University was supported by GM through the GM Collaborative Research Lab at Brown University.

Solidification microstructures and solid-state parallels: Recent developments, future directions

“…Subsequent findings [198][199][200] suggest that Sr may poison the catalytic effects of other impurities, thereby suppressing Si nucleation and increasing the eutectic grain size in commercial alloys. It has also been proposed by Shankar et al [201] that trace amounts of Fe (>30 ppm, which is commonly observed even in high purity Al) may have a strong influence on eutectic growth morphology. Examining this issue in hypoeutectic Al-Si alloys, they claim that nucleation of Al 9 Si 2 Fe 2 in the solute boundary layer just ahead of the primary aluminum phase stimulates nucleation of eutectic silicon and serves to initiate the eutectic reaction.…”

Alloy development and reheating process exploration of Al–Si casting alloys with globular grains for thixoforming

“…This blocky Si phase will re-melt once the material heated to a temperature above the eutectic point. Assuming that thixoforming eliminates the blocky Si, these precipitate will not cause embitterment [32] during usage. After casting, samples 15 ×15 ×15 mm 3 were machined from the billet for the reheating experiments.…”

Reply to discussion on “Nucleation mechanism of eutectic phases in aluminum-silicon hypoeutectic alloys

“…A. [2] They emphasized the role of Fe-rich ␤ particles in initiating eutectic solidification in Al-Si alloys. In a discussion, [3] we objected to their proposal that each eutectic Si plate is nucleated by a ␤ particle.…”

“…The importance they attach to their Figure 7 [1] is emphasized by the fact that in their second article, [2] they published it again ( Figure 4) and again in their Reply [4] as Actually, all but one of the figures in the Reply are republications from the first article. Furthermore, if they really believed that only the initial eutectic Si was caused by a ␤ particle, the very extensive experimental study would seem meaningless.…”

“…MAKHLOUF Dahle and Hillert point to three issues that they have with our Reply [1] to their Discussion. [2] First, they question the statement "Almost every Si flake in the microstructure has a ␤-(Al,Si,Fe) particle attached to its edge" and also Figure 7, [3] and they claim that it does not seem possible to reconcile the micrograph and the statement with the fact that the ␤ phase only initiates the nucleation event of eutectic Si and that further nucleation of Si occurs epitaxially on the solid eutectic Si. Second, they ask "How can one hope to catch that minute ␤ particle by inspecting sections through a bulk sample.…”