Powder Metallurgy Aluminum Alloys Research Articles

Advancements in microstructure, texture characterization, and mechanical properties of powder metallurgy Al-Si-Mg-Fe alloy for engineering applications

Metal powder metallurgy (PM) is widely utilized in the tool and automotive industries due to its near-net forming advantages. While PM aluminum alloys have been explored in numerous studies, their practical engineering applications are still limited. Thus, this research delves into the nuanced aspects of PM Al-Si-Mg-Fe alloy. By employing hot-rolled dynamic recrystallization to control the metallurgical texture and introducing T6 treatment to refine the microstructure. These optimizations aim to enhance the properties of PM aluminum alloy materials. Results revealed that grain coarsening in the PM Al-Si-Mg-Fe alloy hampers the grain boundary strengthening effects, thus limiting the strength. Moreover, the solid-solution treatment applied to the PM specimens efficiently disperses silicon particles within the matrix, preventing the aggregation of silicon particles and the associated brittle effect caused by interface peeling. By implementing a three-stage process, sintering-rolling-T6 treatment, the rolled-T6 exhibited impressive tensile strength (291 MPa) and ductility (17 %), highlighting the excellent engineering applicability of PM Al-alloys. TEM analysis confirmed the presence of nanoprecipitation Al3Mg and Al9Fe2 hard components within the matrix, contributing to the strength enhancement. These findings not only represent a significant milestone in the advancement but also provide valuable references for engineering applications in the field of PM Al-alloys.

Microstructure and mechanical properties of powder metallurgy 2024 aluminum alloy during cold rolling

To improve the low compactness and limited size of powder metallurgy (P/M) aluminum alloy materials, cold rolling deformation on P/M aluminum alloy was carried out in this work. And the microstructure and mechanical properties of P/M aluminum alloy during cold rolling were investigated from multi-dimensional and multi-scale perspectives. The results indicate that the microstructure gradually evolved from the original equiaxial structure to the fiber structure after cold rolling. Also, the grain size decreased with an increase in cumulative reductions. When the cumulative reduction was increased from 0 to 80%, the relative density and tensile strength of the samples increased from 98.31% to 221.94 MPa to 99.04% and 302.88 MPa, respectively. On this basis, the synergetic effect of microstructure densification and deformation strengthening of the P/M 2024 Al alloy during cold rolling was investigated. The improved mechanical properties mainly resulted from the combined effects of the increased microstructural compactness and deformation strengthening.

Microstructure and tensile properties of aluminum powder metallurgy alloy prepared by a novel low-pressure sintering

This paper proposed a novel low-pressure sintering process contraposing to characteristics of pre-alloyed aluminum powders and analyzed its feasibility. The low pressure was set to 0.1 MPa in this study. Meanwhile, 0 MPa and 10 MPa were set as control group. With gas-atomized 2024 aluminum powders as raw material, the microstructure and tensile properties of specimens sintered under three orders of magnitude of pressure (0 MPa, 0.1 MPa and 10 MPa) at two representative temperatures (525 °C and 575 °C) were compared. The results showed that it was difficult for pressureless sintering (0 MPa) to densify pre-alloyed aluminum powders, but low-pressure sintering could. As the liquid phase formed at supersolidus temperature was squeezed out, the loss of alloying elements such as Cu and Mg, which would play an important role in subsequent heat treatment, during low-pressure sintering was apparently less than that of 10 MPa. The density of aluminum sintered under 0.1 MPa at 575 °C was 2.732 g/cm3 and the ultimate tensile strength was 228.16 MPa with ductility of 12 %, which achieved a good balance of plasticity and strength. These findings will bring new insights to the industrialization of aluminum powder metallurgy (APM).

A Micromechanics Analysis for Creep of Powder Metallurgy Aluminum Alloys with Continuous Precipitation

In this study, a micromechanics framework considering both interface diffusion and matrix creep is proposed to analyze the creep behavior of PM alloys. Based on the mean-field micromechanics theory, the creep strain rate induced by interface diffusion in the particulate composite under uniaxial loading is derived. The creep strain is introduced as an eigenstrain into the inclusion, whose rate is expressed in the tensor-form with three non-zero components and naturally satisfies incompressibility. An incremental analysis procedure is employed to model the creep behavior of particulate composites. The aluminum alloy is treated as a composite material, with precipitated particles as the reinforcements. We then adopt the proposed micromechanics approach to study the creep behavior of the powder metallurgy aluminum alloy with continuous precipitation, accounting for both the creep of matrix and the creep induced by interfacial diffusion along the precipitate/matrix interface. The predicted creep curves agree well with experimental results and the explanation for the creep phenomenon has never been proposed before. We have also derived the minimum or steady-state creep rate of the alloy by the micromechanics approach, which turns out to be similar to the expression of improved power-law creep with a threshold stress.

New development of powder metallurgy in automotive industry

The driving force for using powder metallurgy (PM) mostly relies on its near net-shape ability and cost-performance ratio. The automotive application is a main market of PM industry, requiring parts with competitive mechanical or functional performance in a mass production scale. As the automobile technology transforms from traditional internal combustion engine vehicles to new energy vehicles, PM technology is undergoing significant changes in manufacturing and materials development. This review outlines the challenges and opportunities generated by the changes in the automotive technology for PM. Low-cost, high-performance and light-weight are critical aspects for future PM materials development. Therefore, the studies on PM lean-alloyed steel, aluminum alloys, and titanium alloy materials were reviewed. In addition, PM soft magnetic composite applied to new energy vehicles was discussed. Then new opportunities for advanced processing, such as metal injection molding (MIM) and additive manufacturing (AM), in automotive industry were stated. In general, the change in automotive industry raises sufficient development space for PM. While, emerging technologies require more preeminent PM materials. Iron-based parts are still the main PM products due to their mechanical performance and low cost. MIM will occupy the growing market of highly flexible and complex parts. AM opens a door for fast prototyping, great flexibility and customizing at low cost, driving weight and assembling reduction.

A microstructural and mechanical property investigation of a hot upset forged 2xxx series aluminum powder metallurgy alloy reinforced with AlN

Abstract Metal-matrix composites (MMC) of a 2000-series aluminum alloy coupled with AlN were fabricated through a commercially-relevant aluminum powder metallurgy (APM) approach. Cylindrical preforms containing 0–5 vol% AlN were produced to investigate the mechanical properties and microstructure evolution through hot upset forging. Specimen were deformed to a maximum strain of 0.15–1.55 mm/mm at rates of 0.1–1.0 s−1. TEM observations of forged products indicated the Al–AlN interfaces were free of defects and of high quality. Near-full (>99.5% theoretical) densities were observed at 1.40 mm/mm. At this strain, a substantial increase in all tensile properties was observed. An elastic modulus of 77 GPa was realized in a forged product with 5% AlN, accompanied by a 0.2% offset yield strength of 325 MPa and a UTS of at least 400 MPa. Versus an undeformed sample, forged MMC’s exhibited up to a five-fold increase in tensile ductility. Likewise, improvements of up to 98 MPa (57%) in fatigue strength were recorded. Mechanical gains were a result of densification and residual oxide disruption, as well as the enhanced dispersion of the AlN phase.

Different Formation Routes of Pore Structure in Aluminum Powder Metallurgy Alloy.

In powder metallurgy (PM), severe plastic deformation (SPD) is a well-known technological solution to achieve interesting properties. However, the occurrence of pores in the final product may limit these properties. Also, for a given type of microstructure, the stereometric parameters of the pore structures, such as shape (represented by Aspect and Dcircle) and distribution (fshape, and fcircle), decisively affect the final properties. The influence of different processing routes (pressing, sintering and equal channel angular pressing (ECAP)) on pore structures in an aluminum PM alloy is discussed. The nature of porosity, porosity evolution and its behavior is explored. The correlation between pore size and morphology is also considered. The final pore structure parameters (Aspect, Dcircle, fshape, and fcircle) of studied aluminum alloys produced by different processing routes depends on the different formation routes.

Age Hardening of Extruded AA 6005A Aluminium Alloy Powders.

Pre-alloyed micron-sized 6005A Al alloy (AA 6005A) powders, with a Mg/Si atomic ratio of 0.75, obtained by high pressure inert gas atomization were consolidated by uniaxial cold pressing at 200 MPa into cylindrical Al containers and hot extruded at 450, 480 and 500 °C with an extrusion rate of 7:1, followed by artificial T6 precipitation hardening. Ageing conditions were varied between 170 °C and 190 °C and times of 6, 7 and 8 h. The microstructure of the extruded profiles was analysed using X-Ray diffractometry (XRD), light optical microscopy (LOM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Differential scanning calorimetry (DSC) was used to study the possible phase transformations. After our results, the peak-aging hardness condition was achieved at 180 °C for 6 h. Mechanical properties of the powder metallurgy (P/M) aluminium alloys consolidated by hot extrusion were superior to those of the extruded profiles of wrought alloy using conventional ingot metallurgy (I/M) billets. AA 6005A wrought P/M alloy via T6 heat treatment shown yield stress of 317 MPa and elongation of 21% at the extrusion pre-heating temperature of 500 °C.

Effects of process variables on the mechanical and physical properties of an Al–Cu–Mg powder metallurgy alloy

The objective of this research was to analyze the effect sizing and heat treatment had on the properties of a 2xxx series aluminum powder metallurgy alloy. Al–2.3Cu–1.5Mg–0.5Sn was used for experimental work. Natural and artificial aging was studied, as well as various sizing pressures and delay times between process steps (ex. sintering and sizing). It was determined that sizing increased tensile yield strength but decreased tensile ductility and fatigue resistance. Yield strength increased as much as 32% when sized at 400 MPa, whereas ductility and fatigue strength were reduced by up to 51% and 31%, respectively. Delay time between sintering and sizing (T2 samples) did not appear to significantly impact mechanical properties. Through differential scanning calorimetry it was determined that sizing impacted the precipitation of S-type precipitates. It was inferred that there was a preferential tendency for S1-type precipitates to form in sized samples, suppressing full aging to S2-type.

Microstructural evolution of a forged 2XXX series aluminum powder metallurgy alloy

The microstructural response to hot upset forging was studied for a commercially relevant 2000-series aluminum powder metallurgy alloy. Sufficiently large specimens were produced such that the tensile property development was recorded for true compressive forging strains 0 mm/mm to 1.55 mm/mm. Full theoretical density values were obtained and up to a four-fold improvement in tensile ductility was observed. The tensile strength of a sintered-T6 component was measured at 357 MPa, while forging to 1.40 mm/mm increased that to 418 MPa. Microstructural reinforcement was found to be predominantly S-phase precipitates. Prior particle boundaries (PPB) of an unforged specimen were found to be continuously decorated with MgO and Mg2Sn crystallites. Such boundaries in hot forged specimen were discretized into clusters, producing regions of PPB devoid of oxides or other secondary phases. Improvements to mechanical properties were largely attributed to this effect.

Thermal Mechanical Processing of Press and Sinter Al-Cu-Mg-Sn-(AlN) Metal Matrix Composite Materials

The forging of sintered aluminum powder metallurgy alloys is currently viewed as a promising industrial technology for the manufacture of complex engineered products. The powder metallurgy process facilitates the use of admixed ceramic particles to produce aluminum metal matrix composites. However, fundamental data on the thermal-mechanical response of commercially relevant powder metallurgy alloy systems under varying conditions of temperature and strain rate are lacking. To address this constraint, the current study investigates the thermal-mechanical processing response of a family of metal matrix composite materials that employ a commercially exploited base alloy system coupled with admixed additions of aluminum nitride. Industrially-sintered compacts were tested under hot compression using a Gleeble 3500 thermal-mechanical test system to quantify their flow behavior. The nominal workability was assessed as a function of material formulation, sintered preform condition, and processing parameters (temperature and strain rate). Optical metallography and electron backscatter diffraction were used to observe the grain evolution through deformation. Full densification was achieved for materials with ceramic concentrations of 2% volume or less. Zener-Hollomon constituent analyses were also completed to elucidate a more comprehensive understanding the flow behavior inherent to each material. Flow behavior varied directly with the sintered density, which was influenced by the concentration and nature of ceramic particulate.

Industrial Sintering Response and Microstructural Characterization of Aluminum Powder Metallurgy Alloy Alumix 123

In this work, the industrial sintering response of the commercial aluminum powder metallurgy alloy ‘Alumix 123’ has been examined and the resulting microstructure investigated by optical microscopy, scanning electron microscopy, energy-dispersive x-ray spectroscopy, and x-ray diffraction. Alumix 123 is similar in composition to wrought aluminum alloy 2014 and was revealed to develop a sintered density of 92% of theoretical using standard practices for industrial sintering. Microstructural investigations proved that as a result of industrial sintering, a number of embrittling iron-containing intermetallics are developed in addition to the desirable copper-rich intermetallics. To improve the density of sintered components, procedures were developed for secondary processing by ‘sizing’ (repressing) in a laboratory setting. The results showed that sizing to the industry standard reduction in height of 5% only closed a portion of open surface porosity and that higher sizing pressures should be used in applications that are sensitive to this microstructural feature.

Sinterability and characterization of commercial aluminum powder metallurgy alloy Alumix 321

The sinterability of Al-Mg-Si powder metallurgy PM alloy was investigated. This alloy is equivalent to AA6061 and known commercially as Alumix 321. Commercially available Alumix 321 has been sintered in a broad range of temperatures. Green uniaxially pressed compacts in the range of 100–500MPa were sintered at temperatures in the range of 610–640°C. The investigated alloy shows a good sintering response and 98% theoretical density (TD) was achieved. An optimal sintering profile has been selected and the mechanical properties were measured in T1, T6 tempers. Hardness, tensile strength and yield strength values obtained were close to the industrially published values. In addition to the sintering and heat treatment, the microstructure of sintered material has been examined and characterized using optical and scanning electron microscopy.

Stress based fatigue life assessment of sintered steels and aluminium under variable amplitude loading

This paper aims to give an insight into the reliability of fatigue life assessment results for powder metallurgy (PM) components subjected to variable amplitude loading. In this study, notched specimens of two PM steel and two PM aluminium alloys are examined. As the experimental basis, constant amplitude tests with different stress amplitudes and stress ratios (to determine the S–N curves and mean stress sensitivities) as well as service load tests (variable amplitude loading) were carried out. The fatigue life was calculated, applying different modifications of the linear damage accumulation. The results of the experiments and calculations were compared and statistically evaluated. Regarding the resulting scatter, the fatigue life assessment with the modified damage accumulation by Zenner and Liu is recommended. Furthermore, mean relative damage sums are derived, which can be used to correct the fatigue life calculation. For PM steel, these values are very similar to compact steels, whereas they are higher for PM aluminium.

Subsurface modifications in powder metallurgy aluminium alloy composites reinforced with intermetallic MoSi2 particles under dry sliding wear

The effect of dry sliding wear on the subsurface of six AA6061/MoSi2/15p composites processed by powder metallurgy with varying mixing methods (wet blending, rotating cube and ball milling) and reinforcement sizes was investigated. Three regions could be distinguished: the tribolayer or mechanically mixed layer (MML), the elasto-plastically deformed layer, where deflection of material occurs, and the unaffected bulk. The MML was not uniform along the surface and no relation could be found between the size/shape of MML areas and processing variables or applied loads. In the second region, particles close to the MML were found to be fragmented only in the composites processed using low energy. These composites were the only ones to show hardening, together with the similarly processed unreinforced alloy. It can be concluded that, although the subsurface of these composites are noticeably affected by dry wearing through formation of a mechanically mixed layer and material deflection, the ball milled composites do not suffer subsurface hardening and their reinforcing particles do not break during the test. It is also evident from the present research that no simple correlation exists between the size/shape of the tribolayer and deflection parameters and processing variables or applied loads.

Design of Low Cost High Performance Powder Metallurgy Titanium Alloys: Some Basic Considerations

The inexpensive hydrogenated–dehydrogenated (HDH) titanium powder made from the Kroll sponge titanium provides a cost-affordable basis for powder metallurgy (PM) Ti alloy development. The design targets we hope to achieve are low feedstock cost (< $25/kg) including all alloying elements; low fabrication cost based on cold compaction and pressureless sintering, and wrought grades of properties of Ti-6Al-4V in the as-sintered state. Relevant issues are considered. These include alloying with inexpensive elements such as Fe and Si, grain size control during heating, isothermal sintering and cooling, chemical homogeneity of as-sintered microstructure, and simultaneous scavenging of oxygen and chlorine. In addition, it is proposed that achieving 6% of tensile elongation will be adequate for most PM Ti applications, compared to PM steels (normally < 2%), PM aluminium alloys (mostly < 4%) and the requirements for wrought Ti-6Al-4V armour plates (≥ 6%). This will allow the use of HDH Ti powder that contains relatively high oxygen (~0.35wt.%) and direct more efforts towards improving other properties.

Effect of Severe Plastic Deformation on the Characteristics of a PM Aluminum Alloy

The paper deals with the influence of severe plastic deformation on the typical powder metallurgy (PM) microstructural characteristics, such as porosity, of a PM aluminum alloy. A commercial ready-to-press aluminum based powder was used as material to be investigated. After applying different compacting pressures (400, 500, 600 and 700 MPa), specimens were debinded in a ventilated furnace at 400 °C for 60 min. Sintering was carried out in a vacuum furnace at 610 °C for 30 min. The specimens were ECAPed for 1 pass. The dimensional and morphological porosity of investigated materials were measured individually for each pore. Results show that ECAP generates shearing stress breaking down the oxide film; this, coupled to particles deformation under local constraints, enables strong bonding and stability. Therefore, ECAP supports next progressive decreasing of pore size as well as strongly influences both dimensional and morphological porosity characteristics, considering that small pores evolve easily to a circular form. Moreover, ECAP cause strong bonding between adjacent particles, which results in a significant increase of mechanical properties.

Kmax effects on the near-threshold fatigue crack growth of powder-metallurgy aluminum alloys

Fatigue crack growth (FCG) research conducted in the near-threshold regime has identified a room-temperature creep crack growth damage mechanism for a fine-grain powder-metallurgy aluminum alloy (8009). At very low Δ K, an abrupt acceleration in room-temperature FCG rate occurs at high stress ratio and is exacerbated by increased levels of K max ( K max ⩾ 0.4 K Ic). Detailed crack-surface analysis correlates accelerated FCG with the formation of crack-tip process zone micro-void damage. Experimental results show that the near-threshold and K max influenced accelerated crack growth is time and temperature dependent.

Development of Powder Metallurgy Aluminum Alloys with High Strength and High Elevated Temperature Strength

We developed aluminum-based alloys consisting of amorphous, quasicrystalline, nano quasicrystalline plus fcc-Al, nano amorphous plus fcc-Al and glassy phases by a single-roller melt spinning method and a powder-metallurgy processing and examined their structure, thermal, electrical and mechanical properties. The high-pressure gas atomization technique was also used to prepare various aluminum-based alloy powders. Amorphous Al-M-Ni (M: Si, Ge) alloys have good bending ductility and glassy Al-Ln-Ni (Ln: Y, Ce) alloys exhibit a distinct supercooled liquid region. Besides, amorphous or glassy Al-Y-Ni-Co-Sc alloys have the highest strength reported ever before. We also found high strength alloys as Al-Cr-Ce-Co alloys with nano quasicrystalline particles dispersed in fcc-Al phase and Al-M-Fe (M: Ti, V) alloys with nano amorphous particles dispersed in fcc-Al phase. Further, by using the powder metallurgy method, we developed Al-V-Fe and Al-Fe-Cr-Ti alloy rods consisting of quasicrystalline particle dispersed in fcc-Al phase. These aluminum-based alloy rods show high strength, high elevated temperature strength and excellent abrasion resistance.

Dry sliding wear behaviour of some wrought, rapidly solidified powder metallurgy aluminium alloys

Aluminium alloys are increasingly being used in tribological applications, often in composite form, but to date no systematic work has been undertaken on optimising the matrix composition. In particular, it is not clear whether a work-hardened, a precipitation-hardened or dispersion-hardened matrix is optimum. Accordingly, the dry sliding wear behaviour of four aluminium alloys (A2124, A6092 (both precipitation-hardened), A3004 (dispersion-hardened) and A5056 (work-hardened)) was investigated against an M2 steel counterface in the load range 23–140 N and at a fixed sliding speed of 1 m/s. Severe wear was observed for all alloys, with specific wear rates ( K′) in the range 0.31 × 10 −4 to 4.23 × 10 −4 mm 3/(N m). Wear was dominated by transfer of Fe from the counterface for all alloys, which resulted in the formation of a mechanically mixed layer (MML). The relationship between alloy composition, deformation below worn surface and wear resistance is discussed.