Alloy Tensile Research Articles

Effect of trace elements on β-Al5FeSi characteristics, porosity and tensile properties of Al-Si-Cu (319) cast alloys

This study was performed on an Al-6.2% Si-3.7% Cu-0.37% Fe-0.095% Mn (A319.2) alloy, to study the effect of trace elements on the β-Al5FeSi intermetallic phase characteristics observed in the alloy and the resultant tensile properties. The results show that increasing the iron content leads to precipitation of long, branched platelets of the β-Al5FeSi phase. These platelets (or needles as they appear in the microstructure) often result in the formation of large shrinkage cavities due to the inability of the liquid metal to fill the spaces between the branched platelets. The alloy tensile properties are greatly improved by: a) Sr addition in the range 200–400 ppm, b) increasing the Mn/Fe ratio to 0.7, c) addition of 0.08%Be, d) addition of 0.08% Be+ 0.02% Sr. The results indicate that the classic neutralization treatment of using a Mn addition with or without Cr could be replaced by the combined 0.08%Be + 0.02%Sr addition. The latter combination produces a much better improvement in the alloy ductility. The rupture mode changes from transgranular to intergranular as the iron concentration is increased from 0.5% to 1.5%. Fragmentation of the β-Al5FeSi platelets using Sr or Be + Sr, or their transformation into α-Al15(Fe, Mn, Cr)3Si2 in the form of Chinese script or sludge particles (using Mn or Mn + Cr) results in a ductile dimpled rupture surface.

Fragmentation and dissolution of β-Al5FeSi phase during solution heat treatment of Al-13wt%Si-Fe alloys

The dissolution of the platelet/needle-like/β-Al5FeSi phase in unmodified and Sr-modified Al-12wt% Si-0.35 wt% Mg alloys was studied, using three levels of iron viz., 0.5, 1.0, and 1.5%. The alloys were cast in the form of tensile test bars (dendrite arm spacing ∼22 μm) using a Stahl permanent mould (type ASTM B-108). The test bars were solution heat-treated at 540 °C for times up to 200 h. The results indicate that a sufficiently high concentration of Sr (∼350 ppm) breaks down the β-needles into small, thin fragments through (a) splitting of the needles into two halves, and (b) fragmentation due to Si rejection. Minimal β-needle lengths are achieved after 30 h and 10 h for the unmodified and Sr-modified alloys, respectively. The fragmentation process results in stabilising the alloy tensile properties during the period of solution treatment, in that not much variation in the tensile parameters is observed up to 100 h at 540 °C. In the Sr-modified alloys, the YS levels are 50 MPa higher than those obtained from the unmodified alloys treated similarly. Dissolution of the β-phase occurs by decomposition of β-Al5FeSi into Al6Fe and Si particles. While the fragmentation and dissolution of the β-phase is associated with the formation of dimple ruptured surfaces, however, a large proportion of the sample failure occurs by cleavage mode due to persistence of the largest β-phase needles observed in the structure even after solution treatment.

Effects of joint configuration for the arc welding of cast Ti-6Al-4V alloy rods in argon

Statement of problem. Titanium and its alloys are more commonly used in prosthodontics and welding has become the most common modality for their joining. Studies on the welding of titanium and its alloys have not quantified this value, though its importance has been suggested. Purpose. This study compared the strength and properties of the joint achieved at various butt joint gaps by the arc-welding of cast Ti-6Al-4V alloy tensile bars in an argon atmosphere. Material and methods. Forty of 50 specimens were sectioned and welded at four gaps. All specimens underwent tensile testing to determine ultimate tensile strength and percentage elongation, then oxygen analysis and scanning electron microscopy. Results. As no more than 3 samples in any group of 10 actually fractured in the weld itself, a secondary analysis that involved fracture location was initiated. There were no differences in ultimate tensile strength or percentage elongation between specimens with weld gaps of 0.25, 0.50, 0.75, and 1.00 mm and the as-cast specimens. There were no differences in ultimate tensile strength between specimens fracturing in the weld and those fracturing in the gauge in welded specimens; however, as-cast specimens demonstrated a higher ultimate tensile strength than welded specimens that fractured in the weld. Specimens that fractured in the weld site demonstrated less ductility than those that fractured in the gauge in both welded and as-cast specimens, as confirmed by scanning electron microscopy examination. The weld wire showed an oxygen scavenging effect from the as-cast parent alloy. Conclusions. The effects of the joint gap were not significant, whereas the characteristics of the joint itself were, which displayed slightly lower strength and significantly lower ductility (and thus decreased toughness). The arc-welding of cast titanium alloy in argon atmosphere appears to be a reliable and efficient prosthodontic laboratory modality producing predictable results, although titanium casting and joining procedures must be closely controlled to minimize heat effects and oxygen contamination. (J Prosthet Dent 1998;79:291-7.)

低融点アルミニウムろうによるＡ７００３合金のろう付

Brazing of A7003 AI-Zn-Mg alloy is considered to be difficult because of its low melting temperature and high content of oxidation susceptible elements such as Mg and Zn. Obtaining high joint strength by vacuum brazing with conventional fillers, where no flux in used, is practically impossible.In this study, Al-Ge-Si-Mg-Cu and Al-Ge-Si-Mg alloys were examined as brazing fillers for A7003 alloy. These fillers were formed into 100 μm thick foils by PFC (Planer Flow Casting) method and used in the brazing experiment to investigate relation between brazing temperature and joint strength. SEM observation of the brazed interfaces and surface analysis of the specimens were performed.In Al-Ge-Si-Cu-Mg fillers, the joint strength values measured by tensile test dispersed widely, whereas average strength was 310 MPa, which is 78% of A7003 alloy's tensile strength. In Al-Ge-Si-Mg fillers, the joints brazed with the filler of 753 K melting temperature showed 340 MPa of joint strength in average with narrower dispersion.Auger electron spectroscopy (AES) carried out on the surfaces of specimens revealed the following facts ;(1) Before brazing, surface of the alloy is covered with aluminum oxide.(2) After the brazing at 773 K, aluminum oxide converts to magnesium oxide partially.(3) Surface oxide changes to magnesium oxide perfectly after the heating at 823 K.Mg in the fillers therefore acts as wetting agent only in the conditions where the brazing temperature is lower than 773 K, being ineffective at 823 k. This is responsible for the higher strength with narrower dispersion in the joint brazed with the Al-Ge-Si-Mg filler of 753 K of melting temperature.

COMBINED MODE FRACTURE OF A DUCTILE MATERIAL UNDER PLANE STRESS CONDITIONS

Abstract— On the basis of our experimental results on Ly12‐CZ (similar to 2024‐T3) aluminium alloy tensile sheet specimens and Tresca's theory, a fracture criterion for a combined mode crack in ductile materials under plane stress conditions is proposed.

Pore Formation and Its Effect on Mechanical Properties in W—Ni—Fe Heavy Alloy

W–Ni–Fe heavy alloy tensile specimens were sintered at 1450°C for various times up to 44h. The W content varied between 90 and 96 wt-%, and the Ni to Fe weight ratio was 1:1. The specimens are fully densified after 15 min to 1 h of sintering and show high strength and ductility. During the tension test, cracks are formed at the interface between tungsten grains when the grain deformation reaches critical levels. The number of these intergranular cracks increases with deformation until the specimens fracture. When the specimens are over-sintered for 4 and 8 h, large irregular pores are formed with a sharp decrease of strength and ductility. Upon further sintering, the porosity decreases again with a recovery of the mechanical properties. The results demonstrate that small amounts of porosity, even 1 or 2%, can cause drastic reduction of the mechanical properties in tungsten heavy alloys.

Cracking of Zr-2.5 wt% Nb alloy tensile specimens by stray contamination

It is shown that stressed specimens of Zr-2.5 wt% Nb alloy can suffer brittle failure as a result of stress corrosion cracking (SCC) caused by contamination with human perspiration. The SCC is analogous to that previously observed for Zircaloy-2 contaminated with traces of a eutectic mixture of sodium and potassium nitrate and chloride. The chlorides are a primary component of perspiration and the nitrate probably comes from oxidation of organic nitrogenous compounds in perspiration. The contamination is more potent when tests are carried out in impure helium than when carried out in air, presumably through the effect of the atmosphere on the state of the organic component of the contamination.

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Report on a study in the evaluation of gravity die and sandmold designs for aluminum alloy tensile test bars

Report on a study in the evaluation of gravity die and sandmold designs for aluminum alloy tensile test bars