Size Of Intermetallic Particles Research Articles

Crevice Corrosion Initiation and Growth of Die-Cast ADC12 Aluminum Alloy

Die-cast ADC12 (Al-3Cu-10Si) aluminum alloy is widely used because of mechanical properties and castability. In atmospheric environments, crevice corrosion sometimes occurs on ADC12; therefore, improvement of corrosion resistance and elucidation of corrosion mechanisms are needed.As-cast specimens of ADC12 were used in this study. Pure Al sheets were used for comparison. The microstructure of ADC12 was composed of α-Al and Al-Si eutectic phases. Intermetallic particles (IMPs) containing Cu existed. IMPs containing Fe also existed. The size of IMPs was around 1 μm.Crevice was made between a polycarbonate nut and bolt, and immersion test was performed in 0.1 M NaCl. After immersion, the dissolution of α-Al was observed inside the crevice. To ascertain the effect of pH on α-Al phase dissolution, immersion test was carried out in 0.1 M HCl and 0.1 M NaCl (pH 10.0) In 0.1 M HCl, α-Al dissolved, and the corrosion morphology was similar to that inside the crevice.

Effect of the End-of-Life (EOL) Content in High-Pressure Vacuum-Assisted Die Cast (HPVADC) Aural2 (AlSi10Mg) on Corrosion Behaviour

Al cast alloys are widely used in automotive applications due to their high strength-to-weight ratio. The castability of Al alloy is known to be excellent; the idea of implementing the End-of-Life (EOL) Al alloy parts to fabricate new Al alloys is determined to be feasible. In contrast, the fabrication of Al cast alloys with the EOL content increases the propensity of introducing the impurity element to the Al cast alloys. It is expected to affect the microstructure such as the distribution and morphology of intermetallic particles. The mechanical properties of those alloys, also known as the secondary alloys, are comparable to primary alloys, however, the corrosion behaviour of secondary alloys is not fully characterized and understood. It is anticipated that the corrosion behaviour is affected by the EOL content introduced to the Al cast alloys.In this research, HPVADC Aural2 alloy with different EOL contents (0%, 40%, 75%, and 90%) are subjected to various electrochemical characterization techniques and microstructure characterization. Cyclic polarization measurements were conducted on both skin and core parts of the alloys. The breakdown potential (Eb) of the primary alloy was found to be the lowest, however, the potential difference between the breakdown (Eb) and repassivation (Er) of the primary alloy was significantly smaller than the secondary alloys. Potentiostatic polarization was also performed on both skin and core parts to observe the corrosion modes, and it was determined that both initiation and propagation corrosion modes were inter-granular/inter-dendritic corrosion. Galvanostatic polarization measurements were performed, and the behaviour of the potential responses differed between the primary and the secondary alloys, as well as the core and skin. Scanning Vibrating Electrode Technique (SVET) will be performed on the cross-section, skin, and core region to observe the local anodic/cathodic current density. The passive layer characteristics of each EOL alloy will be investigated by X-ray Photoelectron Spectroscopy (XPS). Microstructure analysis through Light Optical Microscope (LOM) and Scanning Electron Microscopy (SEM) was conducted. The distribution of Si eutectic and Fe-containing intermetallic particles on the secondary alloys was found to be different from the primary alloy; the mean size of intermetallic particles observed on the skin in the secondary alloys was higher than the primary alloy. No significant difference was observed at the core region in terms of intermetallic distribution. The morphology and chemistry of intermetallic particles will be further investigated with Energy Dispersive Spectroscopy (EDS).This research is conducted to characterize the effect of EOL content on their microstructures which is essential to understand the corrosion behaviour of the secondary alloys, ultimately enhancing the utilization of EOL parts in the Al cast alloy manufacturing.

Highly dispersed L12-Pt3Fe intermetallic particles supported on single atom Fe-Nx-Cy active sites for enhanced activity and durability towards oxygen reduction

Highly active and durable oxygen reduction reaction (ORR) catalysts with sufficient activity and stability of Pt are beneficial for the commercialization of proton exchange membrane fuel cells. Here we report an effective approach to prepare a composite catalyst comprising of ordered L12-Pt3Fe intermetallic nanoparticles interact with single atom Fe-Nx-Cy active sites. The addition of Fe and the confinement effect of hierarchical porous structure limit the growth of intermetallic particle size (around 2.5 nm). The ligand effect of the electron transfer from Fe to Pt and the synergistic interaction between L12-Pt3Fe and Fe-Nx-Cy work together to reduce oxygen intermediates adsorption and improve kinetics process. Experimentally, the L12-Pt3Fe/CFe-N-C catalyst shows high mass activity and specific activity at 1.010 A/mgPt and 1.166 mA/cm2, respectively, which are 5.8 and 5.1 times higher than those of commercial Pt/C (0.174 A/mgPt and 0.230 mA/cm2). Thanks to the more stable L12 structure, L12-Pt3Fe/CFe-N-C exhibits better durability (14 mV E1/2 loss of L12-Pt3Fe/CFe-N-C and 33 mV E1/2 loss of commercial Pt/C) after 30,000 cycles accelerated stress tests. The strategy to design and prepare small particle Pt-based intermetallic alloys coordinated with M-N-C active sites provides a new direction to obtain low-cost and easily prepared effective ORR catalysts.

Characterization of the anodic oxide layer deposited on severely deformed and aged AA6063 aluminum alloy

The aim of this study was to investigate the effects of severe plastic deformation (SPD) and thermal treatment on the nanostructure and properties of the anodic oxide layer of AA6063. SPD was conducted using up to 6 passes of equal channel angular pressing (ECAP) which was followed by post-deformation aging treatment. Two-step anodization via hybrid pulse voltage was utilized to form highly ordered anodic coatings. Positive pulse and reverse pulse modes were used for the first and second steps of anodization, respectively. Nanostructure, uniformity, porosity, roughness, micro hardness and brightness of the anodic oxide layers were investigated. It was found that with increasing deformation, the size of intermetallic particles decreased which improved the order and uniformity of the Al2O3 layer. This was attributed to increasing micro- and nano-scale orders of anodic structure. The micro-scale order of anodic structure increases due to high density of grain boundaries after SPD. With increasing deformation, two-dimensional ordering in micro and nano-scales was observed. In addition, micro hardness and brightness of coatings were increased and the roughness and porosity were decreased. This may be due to the fact that a more uniform current can establish between anode and cathode during anodization of samples with more significant deformation which leads to uniform and highly ordered anodic layers. In addition, application of aging treatment leads to higher non-uniformity in established current and causes reduced ordering and uniformity of anodic layer in addition to enhanced roughness and porosity and reduction in brightness.

Improving mechanical properties of lean Mg–Zn–Ca alloy for absorbable implants via Double Equal Channel Angular Pressing (D-ECAP)

Mg alloys are suitable materials for biodegradable osteosynthesis implants which stabilize bone fractures as long as the fracture is healing but are absorbed by the human body after they have fulfilled this purpose. However, high degradation rates and/or low strength values can be seen as drawbacks of such alloys. The present study deals with a lean Mg–Zn–Ca alloy which exhibits a desired, low degradation rate and explores the possibilities to improve its mechanical properties by Severe Plastic Deformation (SPD) via Double Equal Channel Angular Pressing (D-ECAP). The effects of different D-ECAP process parameters on the microstructure, mechanical properties and degradation behavior are investigated in detail. The results show that grain refinement during D-ECAP occurs via dynamic recrystallization. Lowering the processing temperature leads to a reduction of the size of the smaller grains of the initial bimodal grain size distribution while a higher degree of deformation (higher number of D-ECAP passes) reduces almost only the area fraction of the larger grains. While the increase in hardness is mainly due to the small size of the recrystallized grains, the tensile strength is additionally determined by the remaining larger grains. Thus, the mechanical properties of the lean Mg–Zn–Ca alloy can be tailored by D-ECAP according to the requirements of the final application. For example, the tensile strength can be increased to more than 370 MPa while maintaining the elongation at fracture at 7%. The degradation rate is not affected by D-ECAP as the process does not change the number or size of intermetallic particles. The optimized mechanical properties, in combination with the low degradation rate, make the D-ECAP-processed alloy very suitable for biomedical applications as absorbable material for osteosynthesis implants.

Mechanical properties enhancement of cast Al-8.5Fe-1.3V-1.7Si (FVS0812) alloy by friction stir processing

This study was conducted to investigate the capability of multi-pass friction stir processing (FSP) on microstructure modification and mechanical properties improvement of FVS0812 alloy. FSP was performed at different rotation speeds (1250, 1600, 2000, and 2500 rpm) and traverse speeds (8, 12, and 25 mm/min) for one, two, and four passes. According to the results, applying single-pass FSP at optimized conditions (i.e. 1600 rpm and 12 mm/min) enhanced the tensile strength, fracture strain, and microhardness of the alloy by about 1020, 1050, and 60%, respectively. This improvement can be mainly attributed to the intense breakage and uniform distribution of θ-Al13Fe4 and α-Al12(Fe,V)3Si intermetallics within the matrix, formation of ultrafine recrystallized grains, and elimination of casting defects. Increasing the number of FSP passes up to four slightly decreased the average size of intermetallic particles, but significantly improved their distribution within the matrix which led to 18 and 200% improvement of tensile strength and fracture strain of one-pass FSPed sample, respectively. The fractography results also revealed that multi-pass FSP has changed the fracture mode of Al-8.5Fe-1.3V-1.7Si alloy from low-energy brittle to a more ductile-dimple fracture.

Evaluating the microstructure and mechanical properties of friction stir processed Al–Si alloy

ABSTRACTIn this study, mechanical behaviour and microstructural evolution in friction stir processing (FSP) of casting hypereutectic A390 aluminium alloy have been investigated. The mechanical behaviour of FSP samples was investigated by measuring the strain rate sensitivity using shear punch testing. The room-temperature shear punch tests were conducted at shear strain rates in the range of 10−4–10−1 s−1. The results indicate that the strain rate sensitivity index increases from about 0.015 to 0.120 for as-cast A390 after third FSP pass and then experiences a further growth in FSP passes. The increase in the grain size and CuAl2 intermetallic particle size result in a reduction in strain sensitivity index as well as shear strength after third FSP pass.

Characterization of fatigue behavior of Al-Li alloy 2099

Experiments and modeling were performed to quantify the microstructure-fatigue properties relationship of wrought aluminum-lithium alloy 2099 (AA2099) plate. Microstructural morphology was examined via optical microscopy, SEM, and TEM techniques. The mechanical properties were determined through monotonic tensile and fully reversed fatigue testing. The rolled AA2099 was shown to have large elongated columnar grains several millimeters long. Metastable secondary phases, T1 and δ′, were observed and provided strength to the material. Fractography determined fatigue cracks initiate from copper-rich constituent particles. These particles ranged from 1 to 25 μm in size, with an average size of 12 μm. The size of these intermetallic Cu-rich particles influenced the fatigue life of AA2099. Lastly, a microstructure-sensitive fatigue model was used to correlate the various effects of intermetallic particle sizes on the fatigue life of AA2099.

Investigation of Zirconium Effect on the Corrosion Resistance of Aluminum Alloy Using Electrochemical Methods and Numerical Simulation in an Acidified Synthetic Sea Salt Solution.

Corrosion resistance of Zr that has been added to an Al alloy (U1070) is higher than that of a commercial Al alloy (A1070). A decreasing number and size of Al3Fe intermetallic particles (IMPs) were observed by electron microprobe analysis and transmission electron microscopy. Based on the numerical corrosion simulation, it was confirmed that decreasing the number and size of IMPs was favorable for improving the corrosion resistance of the Al alloy due to the reduction of the galvanic effect. In addition, Al3Zr was found to be insignificant in promoting galvanic corrosion within the Al matrix. Thus, Zr is an advantageous alloying element for improving the corrosion resistance of the Al alloy.

Friction Stir Processing of Aluminum Alloy A206: Part I—Microstructure Evolution

Friction stir processing (FSP) was applied to plates of cast aluminum A206 alloy. The focus of the work was on the evolution of microstructure during processing, which yielded dramatic decrease in the local grain size of the processed material. Reduction in pore morphology features, as well as intermetallic particle size, was also observed. Friction-stir-processed metal is characterized by a high ratio of high-angle grain boundaries to low-angle boundaries compared to what is observed in the as-cast alloy. Consistent with findings of other investigators, FSP generates a product nugget which has a portion of its structure having an onion skin-type structure that is characterized by a preferred crystallographic texture within individual bands in the nugget.

Fabrication of Mg/Al12Mg17 in-situ surface nanocomposite via friction stir processing

In this study, in-situ magnesium matrix surface nanocomposites were prepared by adding Al particles to an as-cast pure Mg ingot using friction stir processing (FSP). The effects of the number of FSP passes, tool design, rotational and travel speeds were investigated. Microstructural investigations showed a significant grain refinement owing to dynamic recrystallization. According to scanning electron microscopy examinations and X-ray diffraction results, Al12Mg17 intermetallics were formed during FSP due to chemical reaction at the Al-Mg interface. As a result of severe plastic deformation, the intermetallic particles formed at nanometre size. X-ray diffraction showed that the crystalline size of intermetallic particles reached ≤ 50nm, due to high material flow during FSP. The intermetallic formation and grain refining led to an increase in the hardness values 1.5–3 times) that of the as-cast pure Mg ingot.

3D imaging and quantification of porosity and intermetallic particles in strontium modified Al-Si alloys

Al-Si alloys are widely used in the automotive and aerospace industries. Porosity is considered to be a major defect in these cast alloys. In this study, the effect of strontium (Sr) modification on porosity formation and intermetallic formation in Al-Si alloys is quantified using X-ray tomography. Quantitative information such as average pore size, shape, pore distribution and intermetallic particle size distribution were evaluated for Sr modified and unmodified Al-Si alloys. Results show that the addition of 400 ppm of Sr increases the porosity by 10% as compared to unmodified Al-Si alloy. Further, Sr addition increases the average equivalent diameter of pores from 2 μm to 18 μm compared to unmodified alloys. A greater number of larger pores were found in the Sr modified alloy, whereas the number of small sized pores was significantly higher in unmodified alloy. The addition of 400 ppm of Sr results in formation of Al-Si-Sr intermetallics with an average equivalent diameter of 4.5 μm. It can be hypothesised that these intermetallic particles act as heterogeneous sites for pore nucleation and significant further growth of porosity in Sr modified alloys.

Effect of Intermetallic Particle Size and Distribution on the Corrosion of an Mg-Al Alloy

The corrosion rates for Mg alloys are dependent on their composition. In particular, the corrosion resistance is usually increased if the alloying elements remain in solid solution and decreased if the alloying elements are above the solid solution solubility limit [1, 2]. Al additions up to 4 wt. % reduce the corrosion rate [2, 3]. During heat treatment, intermetallic particle (IMP) [4, 5] sizes increase while the area fraction remains relatively constant [4]. The size and spacing of these particles impacts the corrosion behaviour and will likely alter the cathodic reaction rate and corrosion rate as observed in other alloys systems [6]. In Mg-Al alloys, IMPs are more noble than typical Mg-Al alloy solid solutions [7, 8]. The IMPs function as cathodes when coupled with the α-Mg phase [9]. These IMPs support cathodic reduction reactions at faster rates than high purity Mg [7]. The extent of attack is dependent on the composition of the IMP. For instance, the cathodic activity of Al8Mn5 is much greater than that of Mg12Al17 or Al3Mg2 [10, 11]. However, little is known about how the size and spacing of these particles alters the cathodic rates and subsequently affects the corrosion rate. Mg-Al alloy, AZ31B was heat treated at temperatures ranging from 300 to 450 °C for durations ranging from 240 to 604,800 sec to produce samples varying in particle size and spacing. The corrosion behavior was examined in terms of its instantaneous corrosion rate and cathodic kinetics as a function of IMP size and spacing for a fixed area fraction of IMPs. The corrosion resistance was determined utilizing electrochemical impedance spectroscopy (EIS) [3]. The cathodic reaction rate was determined at -1.8 VSCE after 24 hrs immersed at the open circuit potential in 0.6 M NaCl. There was a decrease in both icorr and ic (Figure 1) with increasing particle size and spacing at a fixed area fraction of IMPs. The fast reactions around IMPs were mapped using Scanning Electrochemical Microscopy [12-15]. A non-aqueous electrolyte, such as ethelyne glycol or methanol mixed with a NaCl, was found to slow the kinetics of Mg corrosion while enabling mapping of active corroding sites [16]. The solution of 50 wt% methanol and 50 wt% H2O was found to give the best results. The mediator, hexaammineruthenium(III), Ru(NH3)6Cl3, has successfully been used to map Mg corrosion and was utilized herein [12]. The reduction of Ru(NH3)6Cl3 occurred at actively corroding sites. The subsequent oxidation of Ru(NH3)6Cl3 at the tip provided an indicator of sites where significant cathodic electron transfer reactions occurred [17]. The evolution of the reactivity of an AZ31B surface with time was mapped in 0.1 M NaCl (Figure 2). The regions of high cathodic reactivity are shown to spread across the surface as a function of exposure time. Acknowledgements This work was funded by the Office of Naval Research Grant N000141210967 with Dr. David A. Shifler.

Influence of Multi-Pass Friction Stir Processing on the Corrosion Behavior of an Al-Mg-Si Alloy

The effect of multi-pass (100% overlap) friction stir processing (FSP) on the NaCl-induced atmospheric corrosion behavior of an extruded 6005-T6 aluminum alloy has been studied. Samples were contaminated with 70 and 200 μg/cm2 NaCl and exposed in the presence of 400 ppm CO2 for a time interval of 200–3200 h. The results showed that increasing the number of passes gives rise to several crucial changes in the microstructure of the processed regions. Gravimetric analyses and morphological inspections of the corroded samples revealed that multi-pass FSP has also a significant impact on the NaCl-induced atmospheric corrosion behavior of the FS processed samples. While increasing the number of FSP passes resulted in a reduced extent of pitting corrosion in the stir zone, it induced a significant pitting corrosion attack in the heat affected zone of the samples, which were shown to be linked to a reduction in the size of intermetallic particles in the stir zone of the multi-pass FSP specimens. The results also showed that the cathodic activity of intermetallic particles in this family of Al alloys is size-dependent.

Effect of Lanthanum Doping on the Microstructure Evolution and Intermetallic Compound (IMC) Growth during Thermal Aging of SAC305 Solder Alloy

Sn96.5Ag3Cu0.5 (SAC305) is widely used as lead-free solder for surface mount technology (SMT) card assembly and for ball-grid-array (BGA) interconnection in the microelectronic packaging industry as solder balls and pastes. In this study the effects of Lanthanum (La) doping on SAC305 under thermal aging was investigated as function of intermetallic compounds (IMCs) growth and grain size evolution. The morphology of the microstructure was analyzed under Scanning Electron Microscope (SEM) and optical microscope, the elemental distribution was confirmed by Energy Dispersive Spectroscopy (EDS) and phase identification of the crystalline structure formed during thermal aging was confirmed by x-ray diffraction (XRD). It was found that the microstructure of SAC305 solder alloy changes significantly with addition of La. Quantitative analysis of grain size and intermetallic particle size was performed both for undoped and La-doped SAC305 alloys.

Effect of friction stir processing on the tensile and fatigue behavior of a cast A206 alloy

The microstructure of cast Al alloy A206 was modified using friction stir processing (FSP) to eliminate porosity, break down intermetallic particles and refine the grains. The inference from differential scanning calorimetry is that the nugget region of the as-FSP material contained primarily GP zones. Uniaxial tensile tests and bending fatigue tests were carried out at room temperature on A206 alloy in the cast and T4 conditions and after FSP with different heat treatments — as-FSP, FSP and aging, and FSP with solutionizing and aging. These produced varied microstructures with combinations of pores, grain sizes, precipitate types and particle sizes. The ultimate tensile strength and ductility improved after FSP, while the yield strength showed no improvement. A further inference from differential scanning calorimetry and microscopy was that the yield strength depended more on the matrix heat treatment condition; whereas the UTS was limited more by the size and distribution of intermetallic particles. FSP improved both the total fatigue life and the life to crack initiation. Elimination of pores and reduction of the intermetallic particle size contributed to the increased fatigue life; subsequent heat treatments changed the fatigue life only marginally.

Solidification Behavior of Intensively Sheared Hypoeutectic Al-Si Alloy Liquid

The effect of the processing temperature on the microstructural and mechanical properties of Al-Si (hypoeutectic) alloy solidified from intensively sheared liquid metal has been investigated systematically. Intensive shearing gives a significant refinement in grain size and intermetallic particle size. It also is observed that the morphology of intermetallics, defect bands, and microscopic defects in high-pressure die cast components are affected by intensive shearing the liquid metal. We attempt to discuss the possible mechanism for these effects.

Simultaneous Enhancement of Tensile/Compressive Strength and Ductility of Magnesium Alloy AZ31 Using Carbon Nanotubes

AZ31 nanocomposite containing carbon nanotube (CNT) reinforcement was fabricated using solidification processing followed by hot extrusion. The CNT reinforcement was integrated with AZ31 using an Al foil method. The AZ31 nanocomposite exhibited slightly smaller grain and intermetallic particle sizes than monolithic AZ31, reasonable CNT distribution, dominant (10 - 11) texture in the transverse and longitudinal directions unlike monolithic AZ31, and 48% higher hardness than monolithic AZ31. Compared to monolithic AZ31, the AZ31 nanocomposite exhibited higher 0.2%TYS, UTS, tensile failure strain and tensile work of fracture (WOF) (+10%, +17%, +68% and +92%, respectively). Similarly, compared to monolithic AZ31, the AZ31 nanocomposite exhibited higher 0.2%CYS, UCS, average compressive failure strain and compressive WOF (+58%, +3%, +5% and +17%, respectively). Inclusive of crystallographic texture changes, the effect of CNT integration on the enhancement of tensile and compressive properties of AZ31 is investigated in this paper.

Enhancing tensile/compressive response of magnesium alloy AZ31 by integrating with Al 2O 3 nanoparticles

AZ31 nanocomposite containing Al 2O 3 nanoparticle reinforcement was fabricated using solidification processing followed by hot extrusion. The Al 2O 3 nanoparticle reinforcement was isolated prior to melting by wrapping in Al foil of minimal weight (<0.50 wt% with respect to AZ31 matrix weight). The AZ31 nanocomposite exhibited slightly smaller grain and intermetallic particle sizes than monolithic AZ31, reasonable Al 2O 3 nanoparticle distribution, non-dominant (0 0 0 2) texture in the longitudinal direction unlike monolithic AZ31, and 30% higher hardness than monolithic AZ31. Compared to monolithic AZ31, the AZ31 nanocomposite exhibited higher 0.2%TYS, UTS, failure strain and work of fracture (WOF) (+19%, +21%, +113% and +162%, respectively). Also, compared to monolithic AZ31, the AZ31 nanocomposite exhibited higher 0.2%CYS and UCS, similar failure strain, and higher WOF (+5%, +5%, −4% and +11%, respectively). Inclusive of crystallographic texture changes, the effect of Al 2O 3 nanoparticle integration on the enhancement of tensile and compressive properties of AZ31 is investigated in this paper.

Selective Enhancement of Tensile/Compressive Strength and Ductility of AZ31 Magnesium Alloy via Nano-Al&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt; Reinforcement Integration Method Alteration

Two new AZ31 nanocomposites containing Al2O3 nanoparticle reinforcement were fabricated with different reinforcement integration methods using solidification processing followed by hot extrusion. Each nanocomposite had similar composition (Al and Zn contents), microstructure (grain and intermetallic particle sizes, Al2O3 nanoparticle distribution) and hardness. However, the first nanocomposite had better overall tensile properties compared to the second nanocomposite. Also, the second nanocomposite exhibited better overall compressive properties compared to the first nanocomposite. On the whole, the second nanocomposite was more deformable in tension and compression than the first nanocomposite. The effect of reinforcement integration method on the tensile and compressive properties of the AZ31- Al2O3 nanocomposites is investigated in this paper.