Microstructural Analysis of Cast and Heat-Treated Mg–3.2Ce–2Mn Alloy

Russian Journal of Non-Ferrous Metals - A distingtive eutectic structure with Mn particles observed in as-cast Mg–3.2Ce–2Mn (wt %) alloy was investigated in detail in the present study....     

Two Parameter Weibull Analysis of the Effect of Chemical Modification of Al–7si–0.3 Mg Alloy on Ultimate Tensile Strength

Double oxide films are one of the primary reasons that cause casting defects particularly in dross forming alloys. It is not clear whether the beneficial effect of modification melt treatment in Al–Si alloys is entirely due to the transformation of acicular eutectic Si to fibrous morphology. In the present work, the effect of chemical modification of Al–7Si–0.3 Mg alloy on casting reliability was assessed from the Weibull analysis of tensile strengths. The findings show that the modification melt treatment of Al–Si alloy has a beneficial effect as indicated by consistently higher Weibull modulus. Apart from transformation in the silicon morphology, modifiers decrease the scatter present as a result of various defects, particularly the bi-film, resulting in higher reliability for the modified castings.     

Commencement of Ordering in Al–0.69Mg–0.31Si Alloy

Transactions of the Indian Institute of Metals - Early stages of ordering in dilute Al–0.69(at.%)Mg–0.31(at.%)Si alloy, aged at 373 K for 120 h and 7200 h and...     

Microstructural Characterisations and High Temperature Oxidation Studies of Nanostructured Co–Al Coatings Deposited on Superalloy

The microstructural characterizations and high temperature oxidation of magnetron sputtered Co?CAl coatings on the superalloy substrate have been studied in the present work. FE-SEM/EDS and XRD were used to characterize the morphology and formation of different phases in the coatings, respectively. Thermo gravimetric technique was used to investigate the oxidation of the coatings, in air at 900°C. The growth kinetics of the oxide layers was predicted using weight change of the coated sample measured during oxidation. It was found that the oxidation rate of Co?CAl coated superalloy was lower than that uncoated superalloy due to the formation of continuous dense, adherent and protective oxide scale such as CoO, Al₂O₃, Cr₂O₃, CoCr₂O₄, and CoAl₂O₄ over the surface of the coatings exposed to air at high temperature oxidation, 900°C. The microstructural features and phases of the oxidised coatings were used to elucidate the mechanism of high temperature oxidation.     

Effect of Deep Cryogenic Treatment on Wear and Corrosion Resistance of an Al–Zn–Mg–Cu Alloy

Russian Journal of Non-Ferrous Metals - The 7075 aluminum alloy was subjected to deep cryogenic treatment (DCT) at –196°C with liquid nitrogen for different hours. The wear and corrosion...     

Influence of Microstructure on High Temperature Solid Particle Erosion Behaviour of Ti–6Al–4V Alloy

The present article describes the influence of microstructure i.e. lamellar, bimodal and equiaxed on solid particle erosion behaviour of Ti–6AL–4V alloy at service exposed temperature i.e. 400 °C. Erosion tests have been carried out using an air jet type test rig and Taguchi’s experimental design. From erosion test, it has been observed that impact velocity is the most significant controlling factor influencing the erosion of Ti–6Al–4V alloy followed by impingement angle, size of erodent and microstructural variation.The results indicated that erosion rate of Ti–6Al–4V alloy was less in bimodal microstructure followed by equiaxed and lamellar microstructure.     

Rheo-Extrusion of an Alloy Specially Developed for Rheo Process Based on Al–Zn–Mg–Cu System

This study has been directed towards developing 7xxx aluminum alloy for rheo-extrusion. Rheo extrusion was done by a co-rotating twin-screw extruder as a new semi-solid process for production of 7xxx aluminum alloys with high integrity. A super high-strength aluminum alloy was thermodynamically developed with nominal composition of Al–14Zn–9Mg–5.2Cu. The rheo-formability of alloy had been assessed by thermodynamic criteria and mechanical properties. The newly developed alloy showed good rheo-formability in terms of low temperature sensitivity of solid phase and reasonable mechanical properties. The results showed that optimized mechanical properties and microstructure was obtained at 0.6 solid fraction and 450 rpm for screws. The average grain size changed from 300 by conventional casting to 16 µm by rheo-extrusion process, also shape factor changed from 0.3 to 0.9. The mechanical properties of the rheo-extruded samples at these conditions were: UTS of 682, 621 MPa 0.2 % proof stress and 10 % elongation. Furthermore grain coalescence and columnar growth of solid/liquid interface were the main mechanisms that could deteriorate the rheo-formability. Also results showed that increasing of rotation speed could refine grain size and eliminate the grain coalescence but could not overcome instability of interface.     

Effect of Hot Rolling on Grain Refining Performance of Al–5Ti–1B Master Alloy on Hot Tearing on Al–7Si–3Cu Alloy

It has been known experimentally that TiAl₃ acts as a powerful nucleant for the solidification of aluminum from the melt; however, a full microscopic understanding is still lacking. To improve microscopic understanding, hot rolling technique has been performed to the Al–5Ti–1B alloy and the effect of shape and size of the particles on grain refinement has been studied. The effect of hot rolling of Al–5Ti–1B master alloy on its grain refining performance and hot tearing have been studied by OM, XRD, and SEM. Hot rolling improves the grain refining performance of this master alloy, which is required to reduce hot tearing in Al–7Si–3Cu alloy. The improvement in grain refining performance of Al–5Ti–1B master alloy on rolling is due to the fracture of larger TiAl₃ particles into fine particles during rolling. The presented results illustrate that the morphology of TiAl₃ particles alter from the plate-like structure in the as-cast condition Al–5Ti–1B master alloy to the blocky type after rolling due to the fragmentation of plate-like structures. The grain refining response and effect on hot tearing of Al–7Si–3Cu alloy have been studied with as-cast and rolled Al–5Ti–1B master alloys. The results display hot-rolled master alloys revealing enhanced grain refining performance and minimizing hot tear tendency of the alloy at much lower addition level as compared to as-cast master alloys.     

Study on the Effects of Squeeze Pressure on Mechanical Properties and Wear Characteristics of Near Eutectic Al–Si–Cu–Mg–Ni Piston Alloy with Variable Mg Content

In the present work, the effects of pressure on the wear resistance characteristics, mechanical properties and the microstructures of Al–Si piston alloys that have variable Magnesium (Mg) content are studied. The paper begins with an explanation of the desirable properties of eutectic Al–Si alloys and why these chemical and mechanical properties are desirable in the fabrication of light weight machine components. The methods for further strengthening the alloys using alloying elements such as Ni, Cu and Mg, and applying heat treatment are also discussed. The paper also emphasises on the addition of Magnesium, and compares the traditional gravity die casting with a novel hybrid technology known as squeeze casting. In the results and discussion section, the microstructure properties of the Al–Si both as-cast and after heat treatment conditions are discussed. The mechanical and wear properties as well as the implications of pressure on the alloys are also discussed in details. SEM analyses of wear surface and fracture behavior on the as cast Al–Si alloys and after heat treatment, reveal that squeeze pressure increases fracture ductility as well as resistance to wear; more so upon heat treatment. It is also determined that the hardness and UTS values increases with increase in Magnesium content and reaches the maximum values when Mg content is at 1 % of the alloy’s composition.     

Synthesis of an Intermetallic Alloy Based on 2Cu–Ti–Al: Structure Analysis and Electrophysical Properties

Russian Journal of Non-Ferrous Metals - An intermetallic alloy based on the Heusler phase—Cu2TiAl—has been obtained by self-propagating high-temperature synthesis (SHS) in the...     

Sintering Behaviour and Mechanical Properties of Al–Cu–Mg–Si–Sn Aluminum Alloy

The present study investigates the effect of compaction pressure and sintering temperature on densification response and mechanical properties of the Al–3.8Cu–1Mg–0.8Si–0.3Sn (2712) alloy. The compacts were pressed at 200 and 400 MPa and sintered at temperatures ranging from 570–630°C in vacuum (10^?6 Torr). The objective of the present work is to obtain an optimum sintering conditions for achieving higher sintered densities and mechanical properties. The effect of sintering temperature is evaluated by measuring the sintered density, densification parameter, microstructure, phase changes and mechanical properties. While a higher sintering temperature results in densification enhancement, it also leads to microstructural coarsening. Significant improvement in mechanical properties is obtained through age-hardening of sintered alloy under various ageing conditions (T4, T6 and T8).     

Effect of Aging Time on Mechanical Properties and Wear Characteristics of Near Eutectic Al–Si–Cu–Mg–Ni Piston Alloy

Al–12Si–3Cu–1 Mg–1.78Ni alloy is widely used for piston parts in automobile industry. The present paper investigates the effect of aging time for 1–16 h at 180 °C after solution treatment of the alloy at 500 °C for 5 h, on alloys prepared by gravity casting and squeeze casting. The wear rate of the alloy shows a minimum at an intermediate aging time. The hardness and ultimate tensile strength showed a peak at intermediate aging time. Mechanical properties and wear resistance are found to be better in squeeze cast alloy. The result are explained based on the microstructure developed during casting process and on heat treatment for various durations.     

Effect of Microstructure and Mechanical Properties of Al–Mg Alloy Processed by ECAP at Room Temperature and Cryo Temperature

This research primarily focuses on improving the strength of Al 5083 alloy by both the ECAP and Cryo ECAP methodology. Equal Channel Angular Pressing (ECAP) is one of the best technologies that enable the direct transformation of conventional macro grained metals into sub-micron, ultra-fine and nano grained materials. Fine grain size increases the strength and the fracture toughness of the material and provides the potential for super plastic deformation at moderate temperatures and at high strain rates. The microstructure evolution in Al 5083, subjected to Room Temperature ECAP and Cryo ECAP were analysed. ECAP was carried out using an optimized die with Channel angle ‘?’ = 90°and corner angle ‘Ψ’ = 20° through processing route A and C up to four passes. The results were thoroughly studied using TEM, SEM, and optical microscopic images. Initially the annealed sample had the grain size of 80 µm with the equi-axed grains. In Room Temperature, the hardness values and the mechanical strength were found to be increased from 88 to 410 HV and 306 to 453 MPa after four passes in route A and in route C the strength increased from 390 to 416 MPa after four ECAP passes. Moreover, in Cryo Condition, the sample was processed up to four ECAP passes at route A and route C. The hardness of 153 HV was obtained after four passes in route C and 164 HV obtained after four passes on route A. Additionally, fracture behaviour using SEM, grain size using TEM and crystallite size by X-ray diffraction studies were analyzed. It was observed that the Cryo ECAP showed marginal improvements in mechanical properties relative to the RT ECAP in case of Al 5083.     

Processing of Cu–Al–Ni Alloy by Spray Atomization and Deposition Process

The present work describes a new route for the preparation of Cu–Al–Ni alloy strips via spray atomization and deposition route. The route consists of atomizing liquid Cu–Al–Ni alloy with a jet of argon gas in a closed chamber, at a pressure of 1 MPa. The semi-solid Cu–Al–Ni droplets are subsequently collected on the steel substrate placed vertically below the liquid metal stream in the atomization chamber to form a three-dimensional preform. The deposit produced on the substrate contains ~?5% porosity. The microstructural details of the spray deposited Cu–Al–Ni strips explains particularly the presence of porosity, formation of splats during the flight of spray casting and the associated microstructural evolution in Cu–Al–Ni spray deposit are explained.     

Effect of Barothermal Treatment on the Structure and the Mechanical Properties of a High-Strength Eutectic Al–Zn–Mg–Cu–Ni Aluminum Alloy

The effect of barothermal treatment by hot isostatic pressing (HIP) on the structure and the properties of castings of a promising high-strength cast aluminum alloy, namely, nikalin ATs6N4 based on the Al?Zn–Mg–Cu–Ni system, has been studied using two barothermal treatment regimes different in isothermal holding temperature. It is shown that the casting porosity substantially decreases after barothermal treatment; eutectic phase Al3Ni particles are additionally refined during exposure to the barothermal treatment temperature: the higher the HIP temperature, the more substantial the refinement. The improvement of the casting structure after HIP increases their mechanical properties. It is found, in particular, that the plasticity of the alloy in the state of the maximum hardening increases by a factor of more than 8 as compared to the initial state (from 0.82 to 6.9%).     

The Effect of Bridge Geometry on Microstructure and Texture Evolution During Porthole Die Extrusion of an Al–Mg–Si–Mn–Cr Alloy

Porthole die extrusion is used to produce complex hollow aluminum cross-sections for automotive applications. In a porthole die, the material is first divided into multiple streams which are separated by a bridge, before rejoining in the weld chamber and finally passing through the die orifice. The rejoining of the material in the weld chamber produces lines known as weld lines in the final extruded product. The microstructure along the weld line and its associated quality are strongly influenced by the thermal-mechanical history the material experiences as it passes through the portholes, the weld chamber, and the die orifice, which can be altered by die design and, in particular, the bridge geometry. To study the influence of bridge geometry on weld line microstructure and final quality, a series of porthole die extrusion experiments was conducted using an Al–Mg–Si–Mn–Cr alloy and two different types of bridge geometry (streamlined and flat). The experimental results showed that bridge geometry had a significant effect on the local microstructure and crystallographic texture at the weld line. Specifically, EBSD analysis indicated that the weld line texture associated with a streamlined bridge geometry consisted of a deformation texture (mainly the copper component), while the local texture produced by a flat bridge was a recrystallization texture consisting of Cube, Goss, and Cube_RD texture components. Simulation of the extrusion process, using DEFORM 3D, indicated that the weld line produced using a flat bridge experienced a slightly higher temperature, but much higher equivalent strains than the streamlined case. Material away from the weld line was very similar for both cases, indicating that the effect of the die bridge geometry is localized to the region close to the weld line.

     

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.