Effect of Si content on microstructure and mechanical properties of Al–Si–Mg alloys

Microstructure and mechanical properties of as-cast and as-extruded Al–Si–Mg alloys with different Si content are investigated by tensile test, microstructure observation. High density of Si particles in the Al alloys can induce dynamic recrystallization during hot extrusion and it becomes more matured with an increase in the density of Si particles. The tensile strength of as-cast and as-extruded alloys can be improved with the increase of Si content and hot extrusion make the elongation of alloys increase dramatically. Considerable grain refining effect caused by recrystallization occurred during hot extrusion of S2 (equivalently commercial A356 alloy) and S3 (near eutectic alloy) alloys plays an important role in the improvement of elongation. A good combination of strength and elongation for the as-extruded S3 alloy indicates that near eutectic Al–Si alloys can be hot-extruded to produce aluminum profiles with high performance.     

Cryorolling effect on microstructure and mechanical properties of Fe–25Cr–20Ni austenitic stainless steel

Microstructure and mechanical properties of the Fe–25Cr–20Ni austenitic stainless steel after cryorolling with different reductions were investigated by means of optical, scanning and transmission electron microscopy, X-ray diffraction and mini-tensile testing. High density tangled dislocations and a small amount of deformation twins formed after 30% deformation. After 50% strain, a large amount of deformation twins was generated. Meanwhile, interactions between the twins and dislocations started to happen. As the strain increased to 70%, many deformation twins were produced and the interactions between the twins and dislocations were significantly enhanced. When the cryorolling was 90%, the grain size was refined to the nanometer scale. XRD analysis indicated that the diffraction peaks of the samples became broader with the strain increase. The yield strength and the ultimate strength increased from 305 MPa and 645 MPa (before deformation) to 1502 MPa and 1560 MPa (after 90% deformation), respectively. However, the corresponding elongation decreased from 40.8% to 6.4%. The tensile fracture morphology changed from typical dimple rupture to a mixture of quasi-cleavage and ductile fracture. After 90% deformation, the microhardness was 520 HV, which increased by 100% compared with the original un-deformed sample.     

Effect of Fe and Mn additions on microstructure and mechanical properties of spray-deposited Al–20Si–3Cu–1 Mg alloy

Spray deposition is a novel process which is used to manufacture rapidly solidified bulk and near-net-shape preforms. In this paper, Al–20Si–3Cu–1 Mg alloy was prepared by spray deposition technique. The effect of Fe and Mn additions on microstructure and mechanical properties of spray-deposited Al–20Si–3Cu–1 Mg alloy was investigated. The results show that two kinds of intermetallics, i.e. δ-Al₄FeSi₂ and β-Al₅FeSi, is formed in the microstructure of spray-deposited Al–20Si–5Fe–3Cu–1 Mg alloy. With additions of 5% Fe and 3% Mn to Al–20Si–3Cu–1 Mg alloy, the needle shape of Al–Si–Fe intermetallic phases is substituted by the particle shape of Al₁₅(FeMn)₃Si₂ phases. The presence of the intermetallic phases (δ-Al₄FeSi₂, β-Al₅FeSi and Al₁₅(FeMn)₃Si₂) improves the tensile strengths of the alloy efficiently at both the room and elevated temperatures(300 °C).     

Effect of processing parameters on the microstructure and mechanical properties of Al–steel composite foam

Al–steel composite foams comprise of steel hollow spheres embedded in an aluminum matrix and are processed using a gravity casting technique. The effect of processing parameters such as casting temperature and cooling rate on the microstructure and mechanical behavior was studied to establish structure–property relationships. Results show that the amount and composition of intermetallic phases present in the foam microstructure is directly related to casting temperature and cooling rate. Highest strength and energy absorption were obtained from Al–steel foams with fast solidification rates that minimize the growth of intermetallic phases.     

Effect of heat treatment and Fe content on the microstructure and mechanical properties of die-cast Al–Si–Cu alloys

The effect of solution and ageing heat treatment on the microstructure and mechanical properties of the die-cast Al–9 wt.%Si–3.5 wt.%Cu alloys containing 0.1–1.0 wt.% Fe was investigated. The results showed that the dendritic primary α-Al phase was varied from 20 to 100 μm in size and the globular α-Al grains were smaller than 10 μm in size. The Fe-rich intermetallics exhibited coarse compact or star-like shapes with the sizes from 10 to 20 μm and the fine compact particles at an average size of 0.75 μm. The solution treatment of the alloys could be achieved in a short period of time, typically 30 min at 510 °C, which dissolved the Cu-rich intermetallics into the primary α-Al phase and spheroidised the eutectic Si phase. During the subsequent ageing treatment, numerous fine precipitates of θ′ and Q′ phases were formed to provide effective strengthening to the α-Al phase, significantly improving the mechanical properties. Therefore, Fe content in the die-cast Al–Si–Cu alloys needs to be controlled at a low level in order to obtain the improved ductility and strength under solution and aged condition.     

Manganese dependence of microstructure and mechanical properties in Fe–Mn alloy

Two Fe–Mn alloys with relatively low Mn content were designed. The microstructure characteristics and resultant mechanical properties were investigated in detail by means of electron back-scattered diffraction, transmission electron microscopy and X-ray diffraction. The results show that the formation of α′-martensite is effectively suppressed and the yield strength and total elongation are significantly enhanced by increasing Mn content from 12 to 13 mass%. A great amount of α′-martensite can effectively enhance strain hardening rate, but they deteriorate ductility. The austenite grain is always divided by multiple-variant ?-martensite plate. In addition, the prior austenite grain boundaries and austenite/?-martensite interfaces can act as obstacle to suppress the growth of ?-martensite plates.     

Effects of Cr,Mn, Si,Cu and Zr on microstructure and mechanical properties of high carbon Fe–16Al alloy

Abstract

Effects of alloying elements Cr, Mn, Si, Cu and Zr on the microstructure and mechanical properties of Fe₃Al (Fe–16Al) based alloy containing ～0·5 wt-%C have been investigated. Six alloys were prepared by a combination of air induction melting with flux cover and electroslag refining (ESR). ESR ingots were hot forged and hot rolled at 1373 K and were further characterised with respect to microstructure and mechanical properties. The base alloy and the alloys containing Cr, Mn, Si and Cu exhibit a two phase microstructure of Fe₃AlC_0·5 precipitates in Fe₃Al matrix whereas the alloy containing Zr exhibits a three phase microstructure, the additional phase being Zr rich carbide precipitates. Cr and Mn have high solubility in Fe₃AlC_0·5 precipitates as compared to Fe₃Al matrix whereas Cu and Si have very high solubility in Fe₃Al matrix compared to Fe₃AlC_0·5 precipitate and Zr has very low solubility in both Fe₃Al matrix and Fe₃AlC_0·5 precipitate. No significant improvement in room and high temperature (at 873 K) strengths was observed by addition of these alloying elements. Furthermore, it was observed that addition of these alloying elements has resulted in poor room and high temperature ductility. Addition of Cr, Mn, Si and Cu has resulted in marginal improvement in creep life, whereas Zr improved the creep life significantly from 22·3 to 117 h.     

Effects of complex modificating technique on microstructure and mechanical properties of hypereutectic Al–Si alloys

In this article, the structure of Al-18Si alloy was modified by thermal-rate treatment technique at 930 °C based on the DSC result. The mechanical properties of Al–18Si alloy were improved remarkable by a complex technique with alloying and thermal-rate treatment. A new treating technique named as complex modificating technique was proposed, and the performance of this technique on Al–18Si–1.5Cu–0.6Mg alloy was investigated. The results show that primary Si can be refined when Al–P master alloy was added into the melt at 770 °C after thermal-rate treatment. Compared with the conventional casting technique by which the melt of alloy was unmodified, better refinement effect can be obtained with the combination of alloying and complex modificating technique: the size of primary Si is decreased from 66 to 16 μm, the tensile strength increased by 75.94% and the brinell hardness by 66.59%. Moreover, the mechanism of the complex modificating technique was also discussed.     

Influence of solutionising and aging temperatures on microstructure and mechanical properties of cast Al–Si–Cu alloy

Abstract

This paper presents the influence of solution and aging temperatures on the microstructure and mechanical properties of 319 secondary cast aluminium alloy. Experimental alloy was subjected to different heat treatment cycles. Heat treatments were designed with two solutionising temperatures (504 and 545°C) at two solutionising times (4 and 8 h), followed by quenching in water at 60°C and artificial aging. The artificial aging was carried out at two temperatures (200 and 154°C) for 6 h. The improvement in mechanical properties was obtained with low solution temperature (504°C) for 8 h followed by quenching in water to 60°C and aging at low temperature (154°C). The increase in the solutionising temperature from 504 to 545°C was recommendable only for short solutionising time (4 h). Increase in the aging temperature from 154 to 200°C has led to the increase in hardness with the corresponding decrease in ductility. Aging under unfavourable conditions (prolonged aging at high temperature) caused coarsening of spheroidised eutectic silicon crystals and precipitated particles resulted in deleterious effect on the tensile strength.     

Effect of nickel on the microstructure and mechanical property of die-cast Al–Mg–Si–Mn alloy

The effect of nickel on the microstructure and mechanical properties of a die-cast Al–Mg–Si–Mn alloy has been investigated. The results show that the presence of Ni in the alloy promotes the formation of Ni-rich intermetallics. These occur consistently during solidification in the die-cast Al–Mg–Si–Mn alloy across different levels of Ni content. The Ni-rich intermetallics exhibit dendritic morphology during the primary solidification and lamellar morphology during the eutectic solidification stage. Ni was found to be always associated with iron forming AlFeMnSiNi intermetallics, and no Al₃Ni intermetallic was observed when Ni concentrations were up to 2.06 wt% in the alloy. Although with different morphologies, the Ni-rich intermetallics were identified as the same AlFeMnSiNi phase bearing a typical composition of Al_[100–140](Fe,Mn)_[2–7]SiNi_[4–9]. With increasing Ni content, the spacing of the α-Al–Mg₂Si eutectic phase was enlarged in the Al–Mg–Si–Mn alloy. The addition of Ni to the alloy resulted in a slight increase in the yield strength, but a significant decrease in the elongation. The ultimate tensile strength (UTS) increased slightly from 300 to 320 MPa when a small amount (e.g. 0.16 wt%) of Ni was added to the alloy, but further increase of the Ni content resulted in a decrease of the UTS.     

Effects of Cu content on microstructure and mechanical properties of Al–14.5Si–0.5Mg alloy

This study elucidates how Cu content affects the microstructure and mechanical properties of Al–14.5Si–0.5Mg alloy, by adding 4.65 wt.% and 0.52 wt.% Cu. Different Fe-bearing phases were found in the two alloys. The acicular β-Al₅FeSi was found only in the high-Cu alloy. In the low-Cu alloy, Al₈Mg₃FeSi₆ was the Fe-bearing phase. Tensile testing indicated that the low-Cu alloy containing Al₈Mg₃FeSi₆ had higher UTS and elongation than the high-Cu alloy containing the acicular β-Al₅FeSi. It is believed that the presence of the acicular β-Al₅FeSi in the high-Cu alloy increased the number of crack initiators and brittleness of the alloy. Increasing Cu content in the Al–14.5Si–0.5Mg alloy also promoted solution hardening and precipitation hardening under as-quenched and aging conditions, respectively. The hardness of the high-Cu alloy therefore exceeded that of low-Cu alloy.     

The effects of Mg amount on the microstructure and mechanical properties of Al–Si–Mg alloys

In this study, the effects of magnesium (Mg) addition to A356 aluminum alloy at different amounts on the microstructure and mechanical properties of this alloy were examined. For the experimental studies, three different alloys (0.43, 0.67 and 0.86 wt%) having various amounts of Mg were prepared through casting process in the form of plates. The plates were homogenized and cooled in the furnace. All the samples were treated with aging process (T6) and then tensile samples were prepared from the homogenized samples. The samples treated with T6 process were characterized by optical microscopy, laser confocal microscopy, Scanning Electron Microscope (SEM), Energy Dispersive Spectrometer (EDS) and X-Ray Diffraction (XRD) examinations as well as hardness measurements and tensile tests. The phases which were formed in the microstructures for different amounts of Mg were examined. It was observed that iron-rich intermetallic compounds were also formed in addition to the phases resulting from the aging process. Fe-rich intermetallic compounds, observed from the fracture surfaces, were found to reduce the tensile strength the alloy. The results also indicate that the tensile strength and hardness of the alloy increase with increasing Mg amount.     

Effects of heat input on microstructure and mechanical properties of Fe–2Cr–Mo–0.12C steel

ABSTRACT

Thermal simulated specimens with the heat inputs of 20, 50 and 80?kJ/cm were used to investigate the effects of heat input on the microstructure and mechanical properties of the Fe–2Cr–Mo–0.12C pressure-vessel steel. The results indicated that the microstructures in the coarse-grained heat affected zone of tested steels with various heat inputs were mainly consisted of lath martensite and bainite ferrite. As the heat input increased, the fraction of martensite decreased and the bainite ferrite fraction increased. The toughness (tested at ?40°C) and hardness for the heat input of 50?kJ/cm were 102?J and 346?HV, respectively, which was attributed to the high-volume fraction (60%) of the high-angle grain-boundary and the fine bainite lath.

This paper is part of a thematic issue on Nuclear Materials.     

Effect of heat treatment on microstructure and mechanical properties of Cu–6.9Ni–2.97Al–0.99Fe–1.06Mn alloy

ABSTRACT

The effect of heat treatment on the mechanical properties and microstructures of Cu–6.9Ni–2.97Al–0.99Fe–1.06Mn alloys was investigated. The results show that the microstructure of the as-cast alloy mainly consists of an alpha-copper matrix and γ-phase Ni₃Al particles. The microstructure of the alloy after solution treatment at 950°C for 2?h is a single-phase alpha-copper supersaturated solid solution and the second-phase strengthening disappears. After ageing treatment at 550°C for 6?h, the γ-phase particles are fully precipitated, and the mechanical properties of the alloy are significantly improved. The tensile strength is increased from 305 to 588?MPa. Quasi-cleavage fracture with shallow dimples appeared in the Cu–6.9Ni–2.97Al–0.99Fe–1.06Mn alloy aged at 550°C for 6?h.     

The synergic effects of Sc and Zr on the microstructure and mechanical properties of Al–Si–Mg alloy

In order to clarify the possibility of Zr substitution for Sc on the modification of Al-Si casting alloys, the microstructural evolution and tensile properties of Al-Si-Mg based alloys with different combinations of Sc and Zr contents (Sc + Zr = 0.5 wt.%) were systematically investigated. It was found that 0.5 wt.% Sc addition could refine the microstructure significantly and modify the eutectic Si from plate-like morphology to fiber, which promotes the spheroidization of eutectic Si during heat treatment. When Zr was added to partly replace Sc, the microstructure was first further refined, but was then slightly coarsened with increasing Zr content. Moreover, high Zr content was found to decrease its modification on eutectic Si. It was observed that Zr can also concomitantly improve strength and ductility compared with the alloy modified by Sc only. The improvement of mechanical properties was attributed to microstructural refinement, particularly the modification of eutectic Si and precipitation of secondary nano-scale Al₃(Sc_1 − xZr_x) dispersoids.     

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

In 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.     

Effect of Al and C on structure and mechanical properties of Fe–Al–C alloys

Abstract

Effect of aluminium and carbon content on the microstructure and mechanical properties of Fe–Al–C alloys has been investigated. Alloys were prepared by combination of air induction melting with flux cover (AIMFC) and electroslag remelting (ESR). The ESR ingots were hot forged and hot rolled at 1373 K. As rolled alloys were examined using optical microscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) to understand the microstructure of these alloys. The ternary Fe–Al–C alloys containing 10·5 and 13 wt-%Al showed the presence of three phases: FeAl with disordered bcc structure, Fe₃Al with ordered DO₃ structure and Fe₃AlC_0·5 precipitates with L′1₂ structure. Addition of high concentration of carbon to these alloys resulted in excellent hot workability and superior tensile at room temperature as well as tensile and creep properties at 873 K. An increase in Al content from 9 to 13 wt-% in Fe–Al–C alloys containing the same levels of carbon has no significant influence on strength and creep properties at 873 K, however resulted in significant improvement in room temperature strength accompanied by a reduction in room temperature ductility.     

Microstructure and mechanical properties of Fe–7Al based lightweight steel containing carbon

The effect of carbon on the microstructure and mechanical properties of lightweight steel based on Fe–7 wt-%Al produced by air induction melting with flux cover is investigated. The ingots were hot worked to plates and were characterised. Steel containing 0.02 wt-%C exhibited a single phase microstructure Fe–Al(α), whereas steel containing 0.5 and 1.0 wt-% carbon exhibited a two-phase microstructure containing significant amounts of Fe₃AlC_0.5 precipitates in Fe–Al(α) matrix. Microhardness of the matrix decreases with increasing carbon content due to depletion of aluminium from the matrix to form Fe₃AlC_0.5 carbides. The bulk hardness, room temperature strength increases and tensile elongation decreases with increasing carbon content. However, at 873 K the improvement in strength as well as creep properties with increasing carbon content is marginal.     

Effect of Al on the microstructure and mechanical properties of Mg–6Zn–2Sn–0.5Mn alloy

The microstructure and mechanical properties of Mg–6Zn–2Sn–0.5Mn–xAl (x?=?0, 1, 2, 3) alloy are investigated. The addition of Al leads to the refinement of grain size and the formation of Al₆Mn, Mg₃₂(Al,Zn)₄₉ also forms when the amount of Al is higher than 2?wt-%. Because of the addition of Al, the precipitates in the alloy after ageing treatment are refined. The alloy containing 1?wt-% Al shows good mechanical properties in the as-cast state which is attributed to the refined grains and low volume fraction of large second phases, it also shows high strength after ageing treatment resulted mainly from the homogeneously distributed fine precipitates, the yield strength, ultimate tensile strength and elongation are 183, 310?MPa and 11%, respectively.     

Evolution of microstructure and mechanical properties during quenching and tempering of ultrahigh strength 0.3C Si–Mn–Cr–Mo low alloy steel

Effects of quenching and tempering treatments on the development of microstructure and mechanical properties of ultrahigh strength 0.3C Si–Mn–Cr–Mo low alloy steel were investigated. Samples were austenitized at 1123–1323 K for 2400 s and oil quenched (OQ) to produce mixed microstructures. Tempering was carried out at 473–773 K for 2–3 h. Phase transformation temperatures were measured using dilatometer. The microstructures were characterized using optical and scanning electron microscope. SEM–EDS analysis was carried out to determine the type and size of non-metallic inclusions. Volume percent of retained austenite was measured by X-ray diffraction technique. Hardness, tensile properties, and impact energies were also determined for all heat treated conditions. Fractography of impact specimens were done using stereomicroscope and SEM. The results showed that newly developed steel exhibited peak hardness, yield strength, and tensile strength of about 600 HV, 1760 MPa, and 1900 MPa, respectively, when OQ from 1203 K and tempered in between 473 and 573 K, combined with adequate ductility and impact toughness. Decrease in hardness and strength was observed with increasing tempering temperature whereas the impact energy was stable up to 623 K, however, impact energy was found to decrease above 632 K due to temper martensite embrittlement.