L. Bichler

Onset of Hot Tearing in AE42 Magnesium Alloy

Abstract Magnesium alloy AE42 has long been recognized as a superior high temperature magnesium alloy for aerospace and automotive components. The elevated temperature strength of this alloy is attributed to the Mg-Alx-REy intermetallics on the grain boundaries preventing grain boundary sliding. However, these intermetallics also hinder interdendritic liquid feeding during casting solidification and contribute to the alloys high susceptibility to hot tearing. In this research, the conditions associated with the onset of hot tearing in the AE42 alloy were identified. Thermal analysis suggested that a casting with a hot tear experienced long vulnerable interval, when interdendritic feeding was minimal and the alloy was susceptible to hot tearing. Microscopic analysis revealed the presence of interdendritic shrinkage pores with Al-RE intermetallics at hot-tear nucleation sites. Further, the elastic residual strain measured by neutron diffraction indicates that tensile strain resulting from contraction of the casting during solidification was responsible for opening and propagation of hot tears in the AE42 alloy.

Polynorbornenes Containing Ferrocene Derivatives and Alkyne‐bis(tricarbonylcobalt)

Coordination of dicobalt hexacarbonyl to the alkyne moiety of norbornene complexes containing either ferrocene or η(6) -chlorobenzene-η(5) -cyclopentadienyliron hexafluorophosphate, gave two unique trimetallic complexes available for ROMP. Polymerization of each monomer using Grubbs second generation catalyst gave organoiron/organocobalt polynorbornenes with weight average molecular weights between 55 300 and 69 000 with PDIs between 1.2 and 1.9. Cyclic voltammetric studies of the monomers and polymers at -40 °C showed a reversible reduction for cationic complexes containing η(6) -benzene-η(5) -cyclopentadienyliron and for the dicobalt hexacarbonyl moieties while, a reversible oxidation for the ferrocene containing complex was observed. Thermal analysis showed that the cobalt carbonyl moiety of the polymers degraded near 130 °C; however, the polymeric backbone was stable up to 350 °C. Scanning electron microscopy (SEM) and SEM-EDS indicated that the polymers possessed a fine globular morphology and that the distribution of iron and cobalt atoms was homogenous on the macro-scale.

Micro and nano-sized polysiloxanes containing organoiron moieties

Utilizing organoiron-mediated nucleophilic aromatic substitution, a number of allylamine-containing organoiron complexes were prepared. Amide formation between 1,1′-ferrocene dicarbonyl chloride and allylamine produced a similar ferrocene compound. These materials were subjected to hydrosilation with methyldiethoxyhydrosilane to generate cationic organoiron siloxanes and ferrocene-containing siloxane complexes. Electrochemical analysis of the allylamine and siloxane complexes showed redox couples characteristic of nitrogen-substituted arene-coordinated cyclopentadienyliron complexes. In situ cleavage of the ethoxy groups followed by the addition of H2SO4 resulted in the formation of polymeric materials. Thermal analysis revealed that the cationic organoiron moieties decomposed between 200 °C and 250 °C, whereas the ferrocene moiety decomposed at 110 °C and the backbones of the polymers began to decompose above 400 °C. The polymers displayed glass transition temperatures between 68 °C and 111 °C. Scanning electron microscopy showed that the polymers possessed very different morphologies, ranging from particulates to crystalline.

Microtomographic Analysis of Impact Damage in FRP Composite Laminates: A Comparative Study

With the advancement of testing tools, the ability to characterize mechanical properties of fiber reinforced polymer (FRP) composites under extreme loading scenarios has allowed designers to use these materials in high-level applications more confidently. Conventionally, impact characterization of composite materials is studied via nondestructive techniques such as ultrasonic C-scanning, infrared thermography, X-ray, and acoustography. None of these techniques, however, enable 3D microscale visualization of the damage at different layers of composite laminates. In this paper, a 3D microtomographic technique has been employed to visualize and compare impact damage modes in a set of thermoplastic laminates. The test samples were made of commingled polypropylene (PP) and glass fibers with two different architectures, including the plain woven and unidirectional. Impact testing using a drop-weight tower, followed by postimpact four-point flexural testing and nondestructive tomographic analysis demonstrated a close relationship between the type of fibre architecture and the induced impact damage mechanisms and their extensions.

Effect of TiC Addition on the Microstructure and Mechanical Properties of B319 Alloy

Master alloys of Ti with Aluminum (Al), Boron (B) or Carbon (C) have been of interest to the aluminum foundry industries for grain refinement of Al alloy systems. However, the use of titanium carbide (TiC) inoculants to refine Al–Cu–Si systems has not yet been successful. Thus, this work examined the possibility of grain refining of B319 aluminum alloy by the direct addition of TiC powder into liquid melt. TiC addition levels of 0.01, 0.02, 0.03, 0.05 and 0.1 wt% were examined. The results suggested that the addition of TiC powder to the alloy refined the microstructure and promoted segregation of eutectic phases. Thermal analysis confirmed a decrease in the nucleation temperature of primary α-Al during solidification as TiC concentration increased. Secondary Dendrite Arm Spacing decreased with increasing addition of TiC, resulting in a concomitant increase in the hardness and the yield strength of the as-cast alloy.

Corrosion Behavior of AZ31 Magnesium Alloy in Highly Alkaline Environment

Industrial components made with a magnesium–aluminum alloy AZ31 are often used in diverse engineering applications where component weight, strength, and durability are critical. Similarly as other Mg alloys, however, the AZ31 is susceptible to corrosion in alkaline environments. In this work, corrosion of commercial grade AZ31 alloy plate was examined in potassium hydroxide (KOH) using immersion and potentiodynamic studies. The results suggest that the concentration of Al and Mn in the alloy may govern the kinetics of micro-galvanic corrosion and the initiation of corrosion pits. Further, trace amounts of Ni in the AZ31 alloy were seen to enable formation of Ni(OH)2 surface layer, which may have further accelerated alloy corrosion due to its cracking and void coalescence. The effect of pH on the corrosion behavior of AZ31 was studied with reference to Pourbaix diagrams.

Measurement of Residual Stresses in Linear Friction Welded In-Service Inconel 718 Superalloy

Measurement of residual strains by neutron diffraction of linear friction welded Inconel® 718 (IN 718) superalloy acquired from a mid-service aero-engine disk was undertaken in this study. Residual strain and stress throughout the various weld regions including the heat affected zone (HAZ), thermomechanical affected zone (TMAZ) and dynamically recrystallized zone (DRX) were characterized. The residual stresses were observed to increase from the base material to the weld interface, with a peak stress at the weld interface in all orthogonal directions. The trends for residual stress across the weld are in agreement with other work published in literature for solid state welding of aerospace alloys, where high residual stresses were commonly reported at the weld interface.

Creep performance of wrought AX30 and EZ33 magnesium alloys

Abstract Wrought magnesium alloy bars, sections and tubes have been extensively used in the aerospace, electronics and automotive industries, where component weight is of concern. The operating temperature of these components is typically limited to <100°C, since Mg alloys undergo appreciable creep above this temperature due to grain boundary sliding and plastic deformation leading to intergranular failure. The objective of this study was to investigate the compressive creep performance and microstructure stability of two wrought magnesium alloys (AX30 and EZ33) upon exposure to 175°C and 50 MPa test conditions. The creep behaviour of each alloy was studied using neutron diffraction, as well as classical extensometer techniques. The results suggested that the EZ33 alloy exhibited uniform elastic response with a total plastic deformation of 0·3% after 24 h. In contrast, AX30 exhibited ∼9% strain hardening on the plane, and a total plastic deformation of 1·5% after 24 h. Microstructure analysis revealed that grain size remained constant during creep testing for both alloys. However, the dissolution of Al2Ca intermetallics in the AX30 alloy resulted in the formation of β-Mg17Al12 phase, which contributed to accelerated creep deformation. On a fait un usage considérable de barres, de sections et de tubes corroyés d’alliage de magnésium dans les industries de l’aérospatiale, de l’électronique et de l’automobile, où le poids des pièces est à considérer. La température de fonctionnement de ces pièces est limitée typiquement à moins de 100°C, puisque les alliages de magnésium subissent un fluage appréciable au-dessus de cette température à cause du glissement du joint de grain et de la déformation plastique menant à la rupture intergranulaire. L’objectif de cette étude consistait à examiner le comportement de fluage en compression et la stabilité de la microstructure de deux alliages corroyés de magnésium (AX30 et EZ33) sous les conditions d’essai d’une exposition à 175°C et 50 MPa. On a étudié le comportement de fluage de chaque alliage en utilisant la diffraction des neutrons ainsi que les techniques classiques de l’extensomètre. Les résultats suggèrent une réponse élastique uniforme avec une déformation plastique totale de 0·3% après 24 heures pour l’alliage EZ33. Par contraste, AX30 exhibait ∼9% de durcissement par écrouissage dans le plan () et une déformation plastique totale de 1·5% après 24 heures. L’analyse de la microstructure révélait que la taille de grain demeurait constante lors de l’essai de fluage des deux alliages. Cependant, la dissolution des intermétalliques Al2Ca dans l’alliage AX30 avait pour résultat la formation de la phase Mg17Al12-β, ce qui contribuait à accélérer la déformation par fluage.

Compressive Creep Behaviour of Extruded Mg Alloys at 150 °C

Wrought magnesium alloy bars, sections and tubes have been extensively used in the aerospace, electronics and automotive industries, where component weight is of concern. The operating temperature of these components is typically limited to below 100°C, since appreciable creep relaxation of the wrought alloys takes place above this temperature.

Grain Refinement of B319 Alloy Using Spark Plasma Sintered Al–Ti–C Grain Refiners

The B319 aluminum alloy is a candidate material for automotive applications, where engineers and material designers are seeking to improve vehicle efficiency through vehicle weight reduction. Although the alloy has many desirable properties, such as excellent castability and moderate strength-to-weight ratio, efforts to further enhance the alloy’s strength via the grain refinement approach play a key role to a wider adaptation of the alloy. However, there remain challenges related to the efficient dispersion of inoculating particles in the liquid alloy during casting. The present research has focused on examining the grain refining ability of various novel grain refiners produced via the spark plasma sintering powder metallurgy process. Two novel grain refiners [aluminum–titanium carbide (Al–TiC) and aluminum–titanium–carbon black (Al–Ti–Cb)] were produced at high and low concentrations and then added to the molten B319 alloy. The grain refiners got dispersed within the melt, thus overcoming the need for external melt stirring or treatment. The high concentration formulations for both Al–TiC and Al–Ti–Cb achieved a reduction in the average grain size by 31% and 25%, respectively.