STRUCTURE CHARACTERIZATION AND PRECIPITATION IN TWO Al-Mg-Si-Mn CASTING ALLOYS

Abstract

Structure characterization and precipitation in two Al-Mg-Si-Mn casting alloys Charakterystyka struktury oraz procesy wydzieleniowe w dwóch stopach odlewniczych układu Al-Mg-Si-Mn AbstractThe as-cast structure of permanent mould (PM) (alloy l) and high-pressure die castings (HPDC) (alloy 2) of the AlMg5Si2Mn alloy has been investigated by differential scanning calorimetry, microhardness measurements, transmission electron microscopy, and energy dispersive X-ray analysis. Inside the a-Al grains in both alloys, curved plate-like precipitates were detected in both alloys. Examination of these precipitates revealed a number of features, such as: (1) the composition of the precipitates is very close to the stochiometric Mg 2 Si compound; (2) precipitates are aligned along dislocations; (3) the precipitate density is much higher for high-pressure die castings where the a-Al matrix contains more dislocations than in permanent mould castings; (4) precipitates lie inside the a-Al grains where they are randomly distributed. Between the Mg 2 Si larnellas, precipitates were not observed. Microhardness tests show that the hardness of the alloy cast into a permanent mould is lower than that of a high-pressure die casting. This observation reveals the origin of high strength in an AlMg5Si2Mn alloy subjected to HPDC. Keywords: aluminium casting alloy, precipitates, element distribution, natural hardening Streszczenie Przy wykorzystaniu różnicowej kalorymetrii skaningowej, pomiarów mikrotwardości, elektronowej mikroskopii transmisyjnej oraz mikroanalizy rentgenowskiej zbadano mikrostrukturę stopu AlMg5Si2Mn, odlewanego kokilowo (stop 1) oraz wysokociśnieniowo (stop 2), w stanie wytworzenia (po odlaniu). W obydwu stopach wewnątrz ziaren α-Al roztworu stałego obserwowano zakrzywione wydzielenia płytkowe. Badanie tych wydzieleń pozwoliło na określenie szeregu ich cech, takich jak: (1) stechiometryczne podobieństwo składu chemicznego ze związkiem Mg 2 Si; (2) ustawienie wydzieleń wzdłuż linii dyslokacji; (3) większa gęstość wydzieleń w przypadku

EFFECT OF ADDITIONAL ALLOYING AND HEAT TREATMENT ON THE PHASE COMPOSITION AND MORPHOLOGY IN Al-Mg-Si TYPE CASTING ALLOY

“…HV 0.05 starts to decrease rapidly after the beginning of the solution treatment and stabilizes after 20-40 minutes. Because the indentations were placed in the a-Al, these results indicate the softening of the matrix; therefore, the measured effect is most likely due to the dissolution of the precipitates of the b''-phase (formed during natural aging), as was shown by Boyko et al [23]. In addition, during the time period between 600 and 1200 minutes, the HV gradually increased but did not reach the level of that in the as-cast state sample.…”

DESIGN OF NEW CASTING ALLOYS OF Al-Mg-Si-Mn SYSTEM WITH ALLOYING ADDITIONS, ITS STRUCTURE AND MECHANICAL PROPERTIES

“…On the right, they are connected by a curved line, which could be identified as a dislocation (line 1). In work [8], it was shown that these particles are formed after natural aging as a result of heterogeneous nucleation on the dislocations. These are most likely particles of the b'-Mg 9 Si 5 phase.…”

FEATURES OF STRUCTURE FORMATION AND CHANGES IN THE MECHANICAL PROPERTIES OF CAST Al-Mg-Si-Mn ALLOY WITH THE ADDITION OF (Ti+Zr)

“…The plasticity and the hardness of these alloys may be controlled by the formation of nano-dispersed particles of a second phase within the matrix. The hardening effects result from dislocation interaction, with the precipitates acting as obstacles to the dislocation motion [7,8]. However, the optimal solution treatment vol.…”