Effets des intermétalliques de fer et des porosités sur les propriétés de traction et d impact sur les alliages de coulée Al-Si-Cu et Al-Si-Mg

Abstract

Aluminum-silicon (Al-Si) alloys are an important class of materials that constitute the majority of aluminum cast parts produced, due to their superior properties and excellent casting characteristics. Within this family of alloys, Al-Si-Cu and Al-Si-Mg cast alloys are frequently employed in automotive applications. The commercially popular 319 and 356 alloys, representing these two alloy systems, were selected for study in the present work, with the aim of investigating the effect of iron intermetallics and porosity on the alloy performance. This was carried out through a study of the tensile and impact properties, these being two of the important mechanical properties used in design calculations. Iron, through the precipitation of second phase intermetallic constituents, in particular the platelike P-AlsFeSi phase, is harmful to the alloy properties. Likewise, gas-or shrinkage porosity in castings is also detrimental to the mechanical properties. By determining the optimum alloying, melt processing and solidification parameters (viz., Fe content, Sr modification and cooling rate) required to minimize the harmful effects of porosity and iron intermetallics, and studying their role on the fracture behavior, the fracture mechanism in the alloys could be determined.Castings were prepared from both industrial and experimental 319.2, B319.2 and A356.2 alloy melts, containing Fe levels of 0.2-1.0 wt%. Sr-modified (-200 ppm) melts were also prepared for each alloy Fe level. The end-chilled refractory mold used provided directional solidification and a range of cooling rates (or dendrite arm spacings, DAS) within the same casting. Tensile and impact test samples machined from specimen blanks sectioned from the castings at various heights above the chill end provided DASs of 23-85um. All samples were T6-heat-treated before testing. Tests were carried out employing Instron Universal and Instrumented Charpy testing machines. Optical microscopy, image analysis, SEM and EPMA techniques were used for microstructural and fracture analysis.The results show that the highest cooling rate (23 urn DAS) is the most significant parameter controlling the size and distribution of the P-AlsFeSi phase and porosity in the unmodified 319.2 and A356.2 alloys. Sr modification is more effective in reducing the Pplatelet size at low Fe levels, but increases both porosity volume fraction and pore size significantly. The Mg-containing B319.2 alloy shows reduction in the P-platelet size due to its partial transformation into AlsFeMgsSiô Chinese script particles. In the Sr-modified alloys, increase in the P-platelet size is still observed at some cooling rates. Porosity volume fraction and pore size also decrease with Mg addition.

Neoadjuvant Endocrine Therapy for Estrogen Receptor–Positive Breast Cancer

“…Several ongoing trials are combining endocrine therapy with selective inhibitors of the PI3K/Akt/mTOR/D-cyclin-CDK4/6 pathways in the neoadjuvant setting, such as letrozole with or without the PI3K inhibitor taselisib (LORELEI) and letrozole with or without the CDK4/6 inhibitor palbociclib (PALLET) . Preliminary analysis of a phase 2 trial examining palbociclib combined with anastrozole as neoadjuvant therapy for stage 2 or 3 ER+ breast cancer showed that the addition of a CDK4/6 inhibitor significantly lowers Ki67, suggesting that the addition of CDK4/6 inhibition can improve the efficacy of NET …”

Direct, Nonoxidative Conversion of Methane to Ethylene, Aromatics, and Hydrogen

“…CH 4 is activated on the metal sites forming CH x species, which dimerize to C 2 H y . Subsequent oligomerization on the acidic sites located inside the zeolite pores yields benzene and naphthalene, as well as copious amounts of coke (19)(20)(21). Commercial prospects for this process are further hampered by the instability of zeolites at the very high reaction temperatures.…”