A Study on Hot Tearing Susceptibility of Al–Cu,Al–Mg,and Al–Zn alloys

The present investigation deals with the hot tearing susceptibility of A206, A518, and A713 alloys. The hot tearing tests of the mentioned alloys were conducted at three different pouring temperatures using sand mold casting. Metallic cores designed to facilitate constrained radial contraction of the aforementioned alloys were used for casting. Macroscopic cracks were found in all the samples except in A518 alloy. It was observed that pouring temperatural and grain size have significant effect on crack susceptibility. Among the investigated alloys, A713 was found to be extremely prone to hot tearing. The microstructure characteristics of the alloys were studied using optical and scanning electron microscopy. Relationships between the pouring temperature, grain size and crack lengths of the alloys were also established.     

Nucleation in Zn–Al alloys grain refined with Ti

Abstract

In order to understand more fully the grain refinement of Zn–Al alloys by Ti, the α′ grains in chill cast 7 and 24% Al alloys have been studied by successive polishing and etching of microsections and by scanning electron microscopy of deeply etched specimens.

Idealized models have been deduced for these grains and it appears that lobed forms nucleate and grow preferentially in the 〈111〉 directions of the nucleus cubes. Increased supercooling causes more complex branching. When visible nuclei are absent the 24% Al alloy grains appear to have had a primitive plate-like morphology soon after nucleation.

The results are unique in the field of heterogeneous nucleation because the nuclei are relatively large and have a well-defined crystalline morphology so that their orientations relative to the early grain shapes can be easily studied.

Résumé

Afin de mieux comprendre l'action du Ti sur l'affmage des grains d'alliages Zn–Al, les grain α′ d'alliages à 7 et 24% d'Al, refroidis brusquement après coulée, ont été étuditiés par polissages et attaques successifs de microsections et par microscopie électronique à balayage d'échantil1ons attaques profondément.

Des modèles idéalisés ont été doouits pour ces grains. Il semble que les formes lobées germent et croissent d'une manière privilegiée dans les direction 〈111〉 des germes cubiques. Une surfusion plus prononcée engendre un embranchement plus complexe. Quand il n'y a pas de germes visibles, il semble que les grains de l'alliage à 24% d'Al aient eu une morphologie primitive en forme de plaques peu après la germination.

Les résultats sont uniques dans le domaine de la germination hétérogène parce que les germes sont relativement gros et possèdent une morphologie cristalline bien définie, de telle sorte que leurs orientations par rapport aux formes initiales des grains peuvent être étudiées facilement.     

Effects of Al content on porous Fe–Al alloys

Abstract

Porous Fe–Al alloys with the nominal composition ranging from Fe–20 wt-%Al to Fe–60 wt-%Al have been fabricated by Fe and Al elemental powder reactive synthesis. The effects of the Al content on the pore properties of resultant porous Fe–Al alloys were systematically studied. It has been found that the volume expansion, the open porosity and the permeability can be manipulated by varying the Al content and that their maximum values are reached at Fe–45 wt-%Al. Their mechanical properties suggest that they are strong enough for the filtration applications.     

Isothermal Solidification of an Al–Zn Alloy

In diffusion brazing, a brazing alloy layer thickness introduced into the gap between brazed parts is very small, which hinders the study of the isothermal solidification process. In this work, the isothermal solidification of an Al–Zn alloy is investigated at large volume and mass of the initial liquid that takes part in isothermal solidification. Zinc cylinders are caulked in the holes bored in aluminum cubes. The samples thus assembled are held at 500 ± 10°C for different times. The volume fraction of isothermal solidified crystals has been determined, and the growth rate of isothermal crystals is shown to decrease upon holding. The crystals formed during isothermal solidification width are up to 380 μm and length more than 1 mm. They are observed in the samples that are held more than 2 days. The zinc content in the isothermal solidified crystals corresponds to its mean content in the aluminum solid solution at 490–510°C, according to the Al–Zn phase diagram. The composition of the former liquid that surrounded the crystals during isothermal solidification coincides with the equilibrium composition of the liquid in the Al–Zn system at a temperature of 490–510°C.     

Effect of alloying by transitional refractory metals on the microstructure and thermal stability of Al–5Zn–3Mg alloys

Abstract

The effect of additions of transitional refractory metals on the structure and properties of Al–Zn–Mg alloys, made by ingot and PM routes, was investigated. The strength of the ingot alloys especially is increased by scandium and zirconium. The modifying action of scandium inhibits recrystallisation and precipitation of the fine-grained coherent Al₃(Sc_1–xZr_x) phase. The effect is weaker in PM alloys where the ultra-high cooling rate during high pressure water atomisation produces the fine-grained structure. PM semi-products of the base composition Al–5Zn–3Mg and alloys without scandium are not recrystallised during heating to 500°C, whereas cast alloys of similar composition recrystallised on the hot extrusion stage at 400–450°C. Of the Sc alloys, Al–5Zn–3Mg–0·5Mn–0·7Zr–0·3Sc showed the highest strength (UTS?=?651 MPa, YS?=?596 MPa), whereas of the PM alloys without scandium Al–5Zn–3Mg–0·85Zr–0·22Cr–0·17Ni–0·15Ti alloy showed UTS?=?618 MPa and YS?=?553 MPa. At melt cooling rates of 10⁵–10⁶ K s^–1 the total content of transitional refractory metals must not exceed 1·5–1·7 wt-% and total content (Zn+Mg) should be <8 wt-% at a Zn/Mg ratio of 5:3.     

Effect of modification on the solidification of Al–Si aluminum alloys

The solidification of the AK12 alloy processed by a standard flux and a combined modifying flux, which significantly increases the mechanical properties of the alloy at a significant increase in the modifying effect time, is studied. The experimental results are simulated using the ProCAST software package.     

Influence of thermal storage on microstructure and properties of Sn–9Zn–xIn alloys

Abstract

This study investigated the solidification behaviour and microstructural properties of Sn–9Zn–xIn alloys cooled under various crucible environments (i.e. gypsum or graphite moulds). Sn–9Zn–xIn solder specimens were prepared with the addition of In ranging from 0 to 0·5 wt-%. The specimens were melted at 200°C, poured into gypsum or graphite moulds and then allowed to cool in air. The microstructure, chemical composition and hardness properties of various specimens were then systematically examined. It was found that the microstructure (and hence the mechanical properties) of the solder samples can be controlled by manipulating the variables of the solidification process, such as cooling rate, element diffusion rate, solubility among elements and the crucible environment.

Cette étude a examiné le comportement de solidification et les propriétés de la microstructure des alliages Sn–9Zn–xIn refroidis dans divers creusets (c’est-à-dire des moules en plâtre ou en graphite). On a préparé des spécimens de soudure de Sn–9Zn–xIn avec des additions d’In variant de 0 à 0·5% en poids. Les spécimens étaient fondus à 200°C, coulés dans des moules en plâtre ou en graphite, et ensuite refroidis à l’air. Ensuite, on a systématiquement examiné la microstructure, la composition chimique et la dureté des divers spécimens. On a trouvé que l’on pouvait contrôler la microstructure (et ainsi les propriétés mécaniques) des échantillons de soudure en manipulant les variables du procédé de solidification, comme la vitesse de refroidissement, la vitesse de diffusion de l’élément et la solubilité entre les éléments ainsi que la nature du creuset.     

Macrostructure and Strength of the Al–Zn–Sn Composite Produced by Liquid-Phase Sintering of the Al–Zn Alloy and Pure Tin Powder Mixture

Russian Journal of Non-Ferrous Metals - Features of liquid-phase sintering compacts made of powders of the Al–10Zn alloy and tin of the PO 2 brand, as well as the influence of sintering modes...     

On development of press and sinter Al–Ni–Mg powder metallurgy alloys

Abstract

The objective of this research was to initiate the development of powder metallurgy alloys based on the Al–Ni–Mg system. In doing so, binary (Al–Mg) and ternary (Al–Ni–Mg) blends were prepared, compacted and sintered using elemental and master alloy feedstock powders. Research began with fundamental studies on the sintering response of the base aluminium powder with additions of magnesium. This element proved essential to the development of a well sintered microstructure while promoting the formation of a small nodular phase that appeared to be AlN. In Al–Ni–Mg systems a well sintered structure comprised of α aluminium plus NiAl₃ was produced at the higher sintering temperatures investigated. Of these ternary alloys studied, Al–15Ni–1Mg exhibited mechanical properties that were comparable with existing commercial 'press and sinter' alloys. The processing, reaction sintering and tensile properties of this alloy were also found to be reproducible in an industrial production environment.     

Misoriented dislocation substructures and the fracture of polycrystalline Cu–Al alloys

The evolution of the dislocation substructure in polycrystalline Cu–Al alloys with various grain sizes is studied during deformation to failure. A relation between the fracture of the alloys and the forming misorientation dislocation substructures is revealed. Microcracks in the alloy are found to form along grain boundaries and the boundaries of misoriented dislocation cells and microtwins.     

Influence of minor Zr and Ti on microstructures and properties of Al–8·6Zn–2·5Mg–2·2Cu alloys

Abstract

The effect of minor Zr and Ti elements on microstructures and properties of Al–8·6Zn–2·5Mg–2·2Cu alloys was investigated. The results show that there is no significant change in the grain size by simultaneous addition of Zr and Ti as compared to individual additions of Zr or Ti to Al–8·6Zn–2·5Mg–2·2Cu alloy. The ability of restraining recrystallisation of Al–8·6Zn–2·5Mg–2·2Cu–0·16Zr–0·04Ti alloy is weaker than that of alloy Al–8·6Zn–2·5Mg–2·2Cu–0·16Zr alloy, since Ti and Zr have a poisoning interaction. The corresponding tensile properties, hardness and stress corrosion cracking resistance of the Al–8·6Zn–2·5Mg–2·2Cu–0·16Zr alloy were decreased by addition of Ti.     

Influence of preliminary deformation on the hardening effect upon aging of Al–Cu–Li alloys

The influence of preliminary deformation upon rolling of wedge specimens on the mechanical properties and the structural phase state of Al–Cu–Li alloys are studied by X-ray diffraction and hardness measurements. Strong dependence of the hardening effect upon aging on the reduction upon rolling has been revealed. Deformation weakly influences the hardness and significantly increases the hardening upon aging. Herewith, the hardening effect is nearly absent at the minimum deformation ratio of 1% and increases with its increase. It is demonstrated that the content of T₁ phase increases from 2 to 4% in the range of a preliminary deformation ratio of 6–10% and the content of δ' phase is ~17% at a deformation ratio in the range 1?6% and increases to 18–19% at a deformation ratio of 6–10%. The δ' phase in an alloy contains <20% nanocrystalline particles with 6–20 nm in size, and the remaining part consists of amorphous particles (as detected by X-ray diffraction) <5 nm in size, which precipitate coherently from the matrix and have the same orientation as the nanocrystalline particles and the solid solution.     

Solution Treatment Enhances Both Static and Damping Properties of Al–Si–Mg alloys

The static properties of Al–Si–Mg alloys have been widely studied, but their damping behavior is generally neglected. Although there is an increasing concern regarding the mitigation of vibration, the correlation between the damping properties and the load bearing capacity of an alloy is frequently neglected. This study explores this relationship using A356 alloy as an example. It is concluded that, owing to eutectic Si coarsening/spheroidization, Mg₂Si/π-phase dissolution, and α-Al solution strengthening, the solution treatment can enhance both static (yield strength) and dynamic (damping ratio) mechanical properties.     

Microstructure and Wear Performance of ECAP Processed Cast Al–Zn–Mg Alloys

In the present investigation, wear performance of equal channel angular pressing (ECAP) processed cast Al–Zn–Mg alloys under dry sliding wear conditions was studied against a steel disc. Initially, Al–Zn–Mg alloys (with 5, 10, 15% zinc and 2% magnesium) were ECAP processed. After ECAP, grain size was reduced and enhancement in the hardness was observed. Wear resistance of the alloys increased after ECAP processing. Wear resistance of the alloys also increased when the quantity of the zinc was increased in the alloys. But, wear resistance of all three alloys decreased with increase in the load and the sliding speed. Coefficient of friction of the alloys decreased after ECAP processing. Coefficient of friction of the alloys also decreased when the quantity of the zinc was increased in the alloys. Coefficient of friction of all three alloys increased with increase in the load and the sliding speed. Irrespective of the alloy composition and applied load, worn surfaces of the cast and homogenized samples were composed of plastic deformation, scratches and micro-ploughing. On the other hand, in ECAP processed samples, morphology of the worn surfaces depended on the applied load. Abrasive wear is the main wear mechanism perceived in cast and homogenized samples at all loads. While in ECAP processed samples, the wear mechanism shifted from adhesive and oxidation wear to abrasive wear with increase in the load. Formation of oxide layers on the surface of the sample increased with increase in the ECAP passes. In ECAP processed samples, transfer of iron content from the disc to the sample surface was identified.