A metallographic study of porosity and fracture behavior in relation to the tensile properties in 319.2 end chill castings

Journal Article · Fri Sep 01 00:00:00 EDT 1995 · Metallurgical Transactions, A

DOI:https://doi.org/10.1007/BF02671250· OSTI ID:116047

Samuel, A M; Samuel, F H ^[1]

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1. Univ. of Quebec, Chicoutimi, Quebec (Canada). Dept. of Applied Sciences

A metallographic study of the porosity and fracture behavior in unidirectionally solidified end chill castings of 319.2 aluminum alloy (Al-6.2 pct Si-3.8 pct Cu-0.5 pct Fe-0.14 pct Mn-0.06 pct Mg-0.073 pct Ti) was carried out using optical microscopy and scanning electron microscopy (SEM) to determine their relationship with the tensile properties. The parameters varied in the production of these castings were the hydrogen ({approximately}0.1 and {approximately}0.37 mL/100 g Al), modifier (0 and 300 ppm Sr), and grain refiner (0 and 0.03 wt pct Ti) concentrations, as well as the solidification time, which increased with decreasing distance from the end chill bottom of the casting, giving dendrite arm spacings (DASs) ranging from {approximately}15 to {approximately}95 {micro}m. Image analysis and energy dispersive X-ray (EDX) analysis were employed for quantification of porosity/microstructural constituents and fracture surface analysis (phase identification), respectively. The results showed that the local solidification time (viz. DAS) significantly influences the ductility at low hydrogen levels; at higher levels, however, hydrogen has a more pronounced effect (porosity related) on the drop in ductility. Porosity is mainly observed in the form of elongated pores along the grain boundaries, with Sr increasing the porosity volume percent and grain refining increasing the probability for pore branching. The beneficial effect of Sr modification, however, improves the alloy ductility. Fracture of the Si, {beta}-Al{sub 5}FeSi, {alpha}-Al{sub 15}(Fe,Mn){sub 3}Si{sub 2}, and Al{sub 2}Cu phases takes place within the phase particles rather than at the particle/Al matrix interface. Sensitivity of tensile properties to DAS allows for the use of the latter as an indicator of the expected properties of the alloy.

• Sponsoring Organization: USDOE
• OSTI ID: 116047
• Journal Information: Metallurgical Transactions, A, Vol. 26, Issue 9; Other Information: PBD: Sep 1995
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
ALUMINIUM BASE ALLOYS
POROSITY
FRACTURE PROPERTIES
TENSILE PROPERTIES
SILICON ALLOYS
COPPER ALLOYS
IRON ADDITIONS
MANGANESE ADDITIONS
MAGNESIUM ADDITIONS
TITANIUM ADDITIONS
STRONTIUM ADDITIONS
OPTICAL MICROSCOPY
SCANNING ELECTRON MICROSCOPY
HYDROGEN
DENDRITES
GRAIN BOUNDARIES
INTERFACES