Microstructural Characterization of Beryllium Treated Al-Si Alloys

Abstract

The present study was carried out on B356 and B357 alloys using the thermal analysis technique. Metallographic samples prepared from these castings were examined using optical microscopy and FESEM. Results revealed that beryllium causes partial modification of the eutectic Si, similar to that reported for magnesium additions. Addition of 0.8 wt.% Mg reduces the eutectic temperature by ∼10 ∘ C. During solidification of alloys containing high levels of Fe and Mg, but no Sr, formation of a Be-Fe phase was detected at 611 ∘ C, close to that of -Al. The Be-Fe phase precipitates in script-like form at or close to the -Al 5 SiFe platelets. A new reaction, composed of fine particles of Si and -Fe phase, was observed to occur near the end of solidification in high Mg-, high Fe-, and Be-containing alloys. The amount of this reaction decreased with the addition of Sr. Occasionally, Be-containing phase particles were observed as part of the reaction. Addition of Be has a noticeable effect on decreasing the -Al 5 FeSi platelet length; this effect may be enhanced by addition of Sr. Beryllium addition also results in precipitation of the -Al 5 FeSi phase in nodular form, which lowers its harmful effects on the alloy mechanical properties.

Metallurgical Parameters Controlling the Eutectic Silicon Charateristics in Be-Treated Al-Si-Mg Alloys

“…The greatest refinement is obtained for the Sr-modified alloy A1S with A1BS and C3BS alloys displaying a close degree of refinement, whereas the addition of Be alone reduces the particle size in both A1B and C3B alloys, but not to the extent as that observed with a combined Be + Sr addition. Applying solution heat treatment thereafter produces only a very slight decrease in particle size, however, a slight increase is obtained for alloys A1BS and C3BS; this increase may be attributed to the coarsening of the Si particles with the increase in solution treatment time [ 16 , 17 , 18 , 20 ].…”

“…In Be-containing alloys, the silicon particles are smaller, their aspect ratio is closer to 1, and the small nodular iron-bearing compounds can improve the tensile properties. The effect on decreasing mechanical properties damage is more apparent in the higher Fe level than in the lower Fe content when Be is added [ 18 ].…”

Effect of Si, Mn, Be and Sr Addition on the Tensile Properties of 6061 Type Alloys: Role of Aging Treatment

“…A type-K thermocouple was placed from the bottom of the graphite mold up to half of its height. The total weight of the casting was about 700 g and the solidification rate was estimated as 0.8 °C/s [ 19 ].…”

“…Elsharkawi et al [ 18 ] and Ibrahim et al [ 19 ] carried out extensive studies on the effect of Be addition on the tensile and impact properties of 356 and 357 alloys, popular commercial industrial alloys. The mechanical properties of Be-containing alloy improved significantly due to the alternation of Fe phase shape as well as fragmentation of β-Al 5 SiFe platelets.…”

On the Microstructure, Hardness and Impact Toughness of 356 and 413 Alloys

“…24 In contrast to the work of Ohmori et al, 22 only a single peak was observed at 180°C (356°F), caused by the precipitation of both b 0 and b 00 particles, followed by continuous softening due to progress in the precipitation and coarsening of incoherent b-Mg 2 Si. 25 Tash et al 26 and Moustafa et al 27 found that the 319 alloy hardness first increased with an increase in aging temperature up to 180°C (356°F) and thereafter decreased as the aging temperature was increased. The increase in hardness with the addition of Cu and Mg may be attributed to the formation of the hard and brittle (metastable) intermetallic Al 2 Cu and Al 2 CuMg phases, as well as to an increased bonding of the Si particles with the matrix, where the thermal energy is sufficient to precipitate such intermediate phases.…”