Sc and Sc–Zr effects on microstructure and mechanical properties of Be–Al alloy

Herein, we investigated the effects of Sc and Sc–Zr on the microstructure and mechanical properties of Be–Al alloy, showing that Sc alloying resulted in Be grain refinement and reduced the secondary dendritic arm spacing (SDAS) of these grains by 1/3, whereas Sc–Zr alloying further decreased the SDAS to 7.5?µm and afforded equiaxed/cellular-like morphology with further refined Be grains. The above alloying resulted in the formation of intermetallic compounds (Be₁₃Sc, Be₁₃Zr, and Al₃(Sc_1–xZr_x)), increasing the macrohardness of the Be–Al alloy, with the microhardness and elastic modulus of the Be phase increasing to a larger extent than those of Al. Importantly, Sc–Zr alloying resulted in better microstructure modification and mechanical reinforcement than Sc alloying.     

Effects of Sc(Zr) on the microstructure and mechanical properties of as-cast Al–Mg alloys

Both the addition of 0.6% Sc and simultaneous addition of 0.2% Sc and 0.1% Zr exerted a remarkable effect on grain refinement of as-cast Al–Mg alloys, changing typical dendritic microstructure into fine equiaxed grains. Such effect was found to be related to the formation of primary particles, which acted as heterogeneous nucleation sites for α-Al matrix during solidification. Primary particles formed in Al–Mg–Sc–Zr alloy could be identified as the eutectic structure consisting of multilayer of ‘Al₃(Sc,Zr)?+?α-Al?+?Al₃(Sc,Zr)’, with a ‘cellular-dendritic’ mode of growth. In addition, an attractive comprehensive property of as-cast Al–5Mg alloy due to the addition of 0.2% Sc and 0.1% Zr was obtained.     

Effect of predeformation on microstructure and mechanical properties of Al–Cu–Li–Zr alloy containing Sc

Abstract

The effects of prior cold deformation on the microstructures and the room temperature mechanical properties of an Al–3·5Cu–1·5Li–0·22(Sc + Zr) alloy have been observed by using TEM and tensile test at room temperature. The results show that the alloy has the character of aging hardening, and the major phase of precipitation and strengthening is T₁ phase. The result also show that prior cold deformation leads to more dispersive and uniform distribution of T₁ precipitations. It accelerates aging response, causes earlier aging peak occurrence, and enhances strength greatly. However, the plasticity of the alloy is declined with prior cold deformation. In contrast, excessive prior cold deformation causes coarsening and heterogeneous distribution of T₁ phase. It also reduces the strength of the alloy, therefore, influences the composite properties of the alloy. The favourable prior cold deformation is about 3·5% under the experimental condition.     

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.     

Effects of trace Er addition on the microstructure and mechanical properties of Mg–Zn–Zr alloy

The effects of trace Er addition on the microstructure in Mg–9Zn–0.6Zr alloy during casting, homogenization, pre-heating, and hot extrusion processes were examined. The mechanical properties of alloys with and without Er were compared. The results showed that Er exhibited a lower solubility in solid magnesium and formed thermally stable Er- and Zn-bearing compounds. The Er-bearing alloy exhibited a considerably improved deformability, as well as a fine and uniform microstructure. Moreover, dynamic precipitation of fine MgZn₂ particles with a modified spherical morphology occurred during hot extrusion, resulting in a tensile yield strength of 313 MPa and a high elongation to failure value of 22%. Further aging of the Er-bearing alloy led to an increment of another 30 MPa in yield strength. In addition, Er markedly increased the thermal stability of the alloy structure.     

Effects of solution treatment on the microstructure and mechanical properties of Al–Cu–Mg–Ag alloy

The effects of solution treatment on the microstructure and mechanical properties of Al–Cu–Mg–Ag alloy were studied by optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive X-ray (EDX), differential scanning calorimeter (DSC), transmission electron microscopy (TEM) and tensile test, respectively. The results show that the mechanical property increases and then decreases with increasing the solution temperature. And the residual phases are dissolved into the matrix gradually, the number fraction of the precipitation and the size of recrystallized grains increase. Compared to the solution temperature, the solution holding time has less effect on the microstructure and the mechanical properties of Al–Cu–Mg–Ag alloy. The overburnt temperature of Al–Cu–Mg–Ag alloy is 525 °C. The yield strength and the elongation get the best when the alloy is solution treated at 515 °C for 1.5 h, is 504 MPa and 12.2% respectively. The fracture mechanism of the samples is ductile fracture.     

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.     

The influences of rare earth content on the microstructure and mechanical properties of Mg–7Zn–5Al alloy

The influences of rare earth (RE) on the microstructure and mechanical properties of Mg–7Zn–5Al alloy were studied. The results indicate that both the dendrite and grain size of the alloy can be refined by low RE addition. The Al₂REZn₂ phase will be formed with increasing the RE content, however the high RE addition results in the grain coarsening in the alloy due to the decrease of the contribution of Al and Zn solutes on the grain refinement. The strengthening and weakening mechanisms caused by RE addition only lead to the obviously improve on the room temperature ultimate tensile strength. The mechanical properties of the studied alloys can be improved by aging treatment, and the aged Mg–7Zn–5Al–2RE alloy exhibits optimal mechanical properties at room temperature.     

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.     

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.     

Effects of yttrium and heat treatment on the microstructure and tensile properties of Al–7.5Si–0.5Mg alloy

The effects of yttrium (Y) additions (0, 0.1, and 0.3 wt.%) and T6 heat treatment on the microstructure and tensile properties of Al–7.5Si–0.5Mg alloy have been investigated in the present work. The microstructures and fracture surfaces of as-cast and heat treated samples were examined by scanning electron microscopy (SEM). It was found that Y modified the eutectic silicon from a coarse plate-like and acicular structure to a fine branched and some fibrous one with a better uniform distribution. In addition, T6 heat treatment played a crucial role in the fragmentation and spheroidization of eutectic silicon, especially in the well modified alloys. The tensile properties were improved by the addition of Y followed by the T6 heat treatment, and a good combination of ultimate tensile strength (353 MPa), yield strength (287 MPa) and elongation (12.1%) was obtained when the Y addition was 0.3 wt.%. Furthermore, fractographic examinations revealed that dimple-like mechanism was responsible for ductile fracture.     

Effect of precipitates on properties of cold-rolled Al–Mg–Si–Sc–Zr alloy with higher temperature aging

The aging hardening behaviours of the cold-rolled Al–Mg–Si–Sc–Zr alloy were investigated. The microstructure, hardness and electrical conductivity (EC) of the Al–Mg–Si–Sc–Zr alloy were measured. The relationship between the microstructure and the properties of the Al–Mg–Si–Sc–Zr alloy with cold-rolling and aging processes was studied. The result shows that the addition of Sc and Zr elements significantly refines the grains of the Al–Mg–Si alloy during casting. The cold rolling promotes the Al–Sc(Zr) precipitation. The precipitate strengthening increases with increasing roll reduction. The EC of the cold rolling?+?aging Al–Mg–Si–Sc–Zr alloy increases with increasing rolling reductions. The combination effects of the precipitation hardening and DRX softening during the aging process lead to the similar peak hardness values of around 70?HV of the rolled Al–Mg–Si–Sc–Zr alloy with the different reductions.     

Atomic bonding and mechanical properties of Al–Li–Zr alloy

The atomic bonding of Al–Li alloy with minor Zr is calculated according to the “Empirical Electronic Theory in Solids”. The result shows that the stronger interaction between Al and Zr atoms, which leads to form the Al–Zr segregation regions, promotes the precipitation of Al₃Zr particles and produces a remarkable refinement of Al₃Li grains in the alloy. Because there are the strongest covalent Al–Zr bonds in Al₃Zr and Al₃(Zr, Li) particles, these covalent bonds can cause a great resistance for dislocation movement, and is favorable to strengthen the alloy. On the other hand, with precipitating the Al₃(Zr, Li) particles, it causes the coherent interphase boundary energy of Al/Al₃Li to decrease, and atomic bonding is well matched in between the interface of two phases.     

Influence of equal channel angular extrusion processing parameters on the microstructure and mechanical properties of Mg–Al–Y–Zn alloy

An as-cast Mg–Al–Y–Zn alloy was successfully processed by equal channel angular extrusion (ECAE) in the temperature range of 225–400 °C, and the influences of processing temperature on the microstructure and mechanical properties were investigated. The use of back pressure during one-pass ECAE of Mg–Al–Y–Zn alloy was favorable for eliminating the undeformed area in the billet. At the processing temperature below 250 °C, the microstructures were characterized by unrecrystallised structure and the precipitated phase Mg₁₇Al₁₂ was elongated along the extrusion direction. With increasing processing temperature to 350 °C, a large number of recrystallised grains were obtained. Increasing processing temperature promoted workability but led to decrease in the strength of Mg–Al–Y–Zn alloy. Then billets of as-cast Mg–Al–Y–Zn alloy were extruded at different numbers of ECAE passes. It was found that the microstructure was effectively refined by ECAE and mechanical properties were improved with numbers of ECAE passes increasing from one-pass to four passes. However, strengths decreased slightly after five passes though the grain size decreased considerably.     

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).     

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.     

Microstructure and mechanical properties of Al–Si cast alloy with additions of Zr–V–Ti

The microstructure and tensile properties at temperatures up to 300 °C of an experimental Al–7Si–1Cu–0.5Mg (wt.%) cast alloy with additions of Ti, V and Zr were assessed and compared with those of the commercial A380 grade. The microstructure of both alloys consisted of Al dendrites surrounded by Al–Si eutectic containing, within its structure, the ternary Al–Al₂Cu–Si phase. Whereas the Al₁₅(FeCrMn)₃Si₂ phases were present in the A380 alloy, Ti/Zr/V together with Al and Si phases, Al(ZrTiV)Si, were identified in the experimental alloy. As a result of chemistry modification the experimental alloy achieved from 20% to 40% higher strength and from 1.5 to 5 times higher ductility than the A380 reference grade. The role of chemistry in improving the alloy thermal stability is discussed.     

Effect of consolidation temperature on mechanical properties of rapidly solidified Al–7Mg–1 Zr alloy

Abstract

The mechanical properties achieved via the extrusion of non-degassed billets prepared from an inert gas atomised powder of nominal composition Al–7Mg–lZr are reported. The alloy was extruded over the temperature range 350–550°C and the tensile mechanical properties and plane strain fracture toughness were evaluated. It was found that the yield strength remained fairly constant over the entire temperature range, with only a small decrease in strength observed at the highest extrusion temperature. The strength could be related to microstructure using standard models for solid solution, dispersoid, and substructural strengthening mechanisms, and the last was found to make the greatest contribution. The sensitivity of strength to subgrain size was found to be nearly three times higher than that for pure Al. The optimum combination of strength and fracture toughness was obtained for extrusion at 500°C (yield strength 400 MN m^?2; T–L K_Iv 21 MN m^?3; elongation 20%). The poor values of K_lv obtained at other temperatures were attributed to coarse dispersoids (highest extrusion temperature), undeformed powder particles (lowest extrusion temperature), and inhomogeneous dispersoid distributions (intermediate temperatures). It is concluded that extrusion process control plays an important role in determining the mechanical properties of consolidated rapidly solidified powders. Considering the excellent ductility and toughness obtained, vacuum degassing before extrusion may not be essential in the processing of inert gas atomised powders of a non heat treatable composition.

MST/1721     

Effects of ECAE temperature and billet orientation on the microstructure,texture evolution and mechanical properties of a Mg–Zn–Y–Zr alloy

Single-pass equal channel angular extrusion (ECAE) experiments of an extruded Mg–Zn–Y–Zr alloy with an intense initial basal texture were performed in two inter-perpendicular billet orientations and at 473 and 623 K. The study was aimed to determine the effects of ECAE temperature and billet orientation on the microstructure, texture evolution and mechanical properties of the ECAEed alloy. It was found that the grain refinement achieved through the single-pass ECAE in the Orient-I billet orientation (the normal direction (ND) of the extruded plate parallel with the ECAE exit direction) was more effective than that in the Orient-II billet orientation (the ND of the extruded plate perpendicular to the ECAE exit direction). The average grain sizes after ECAE at 473 K were much smaller than those after ECAE at 623 K. The pole figures of the alloy ECAEed at 473 K showed that most of the basal planes in the Orient-I and Orient-II samples were inclined about 40° and 35°, respectively, with respect to the longitudinal direction of the ECAE extrudate. However, for the alloy ECAEed at 623 K, most of the basal planes were parallel with the longitudinal direction of the ECAE extrudate. It was remarkable that the yield strengths of the alloy ECAEed at 473 K were lower than those at 623 K. The peculiar relationship between ECAE temperature and the mechanical properties of the alloy was ascribed to the texture evolution during ECAE.