Al11RE3 Phase Research Articles

Microstructural evolution mechanism and mechanical properties of La and Gd on AZ91 alloy: Experiments and first-principles calculations

The morphology and thermal stability of the Al-RE phase in Mg-Al-RE alloys are critical to their mechanical properties, particularly at elevated temperatures. In this study, AZ91, AZ91–2La, and AZ91–2La-0.6Gd alloys were prepared via gravity casting and characterized using optical microscopy (OM), scanning electron microscopy (SEM), X-ray diffraction (XRD), energy-dispersive spectroscopy (EDS) and transmission electron microscopy (TEM). The results indicate that adding La reduces the amount of the Mg17Al12 phase and introduces a long acicular Al11La3 phase. Further addition of minor amounts of Gd transforms the long acicular Al11La3 phase into a short rod-like Al11RE3 phase. Tensile tests and fracture analyses at both room and elevated temperatures reveal that the AZ91–2La-0.6Gd alloy exhibits exceptional tensile properties. First-principles calculations were used to study the modification mechanism of Gd atoms on the Al11La3 phase. Adsorption calculations show that Gd atoms stably adsorb on the Al11La3 (001) growth surface, altering its growth characteristics. These calculations also investigated the thermal stability and formation enthalpy of intermetallic phases in Mg-Al-La-Gd alloys. Additionally, the complex alloying reactions during the solidification of the Mg-Al-La-Gd multi-element alloy system were simplified. This study provides new insights into the interaction mechanisms of rare earth (RE) elements in Mg-Al series alloys. It also offers a new approach for designing heat-resistant Mg-Al-RE alloys.

Systematic First-Principles Investigations of the Nucleation, Growth, and Surface Properties of Al11RE3 Second-Phase Particles in Al-Based Alloys

At room temperature, Al alloys have excellent mechanical properties and are widely used in automotive, electronics, aerospace and other fields, but it is difficult to maintain this advantage in the middle and high temperature ranges. To address this issue, second-phase Al11RE3 (RE represents rare earth element) was introduced into a Al-Mg-RE alloy as its primary constituent. By incorporating RE elements as additives, this material exhibits exceptional mechanical and thermal properties at elevated temperatures. Based on first principles and quasi-harmonic approximation (QHA), the nucleation growth mechanism and surface properties of second-phase Al11RE3 were studied in this paper. The interfacial energy γα/β, strain energy ΔECS and chemical driving force ΔGV of Al11RE3 were obtained. Models1, 4, and 6 have better properties of para-site connections than inter-site connections. It is found that the resistances of particle nucleation, interface energy γα/β and strain energy ΔECS, first increase and then decrease with increased atomic number REs, but they are much smaller than the chemical driving force ΔGV. A reduced chemical driving force and a diminished nucleation radius R* are more favorable for the process of nucleation. The addition of Sc is the most unfavorable for nucleation, and La has the strongest nucleating ability, which gradually decreases as the atomic number of the lanthanide element increases. The nucleation ability of the Al11RE3 phase decreases with increasing temperature, which is consistent with the experiments. The nucleation radius R* also increases with increasing temperature, indicating that the nucleation ability decreases as the atomic number of the lanthanide elements increases. Since the smaller the nucleation radius R* the easier the nucleation, compared with model4 and 6, model1 has a smaller nucleation radius R* and the smallest increment. Thus, model1 is more prominent in the nucleation mechanism. In the particle growth study, the smaller the diffusion activation energy Q, the faster the diffusion rate in the Al matrix, and hence the higher the coiling rate, which promotes the growth of second-phase particles. The diffusion activation energy Q decreases sequentially from La to Ce and then increases with atomic number. The coarsening rate KLSW of the Al11RE3 phase in models1, 4, and 6 increased with increasing temperature, which promoted the growth of particles. This paper is intended to provide a solid theoretical basis for the production and application of aluminum alloy at high temperatures.

Microstructure and Mechanical Properties of Mg-Al-La-Mn Composites Reinforced by AlN Particles.

The Mg-Al-RE series heat-resistant magnesium alloys are applied in automotive engine and transmission system components due to their high-temperature performance. However, after serving at a high temperature for a long time, the Al11RE3 phase coarsened and even decomposed, while the Mg17Al12 phase grew and dissolved, which limits the service temperature of Mg-Al-RE series heat-resistant magnesium alloys to a maximum of 175 °C. In this study, a new preparation method for in situ AlN particles was presented. The AlN/Mg-4Al-4La-0.3Mn composites were prepared by a master alloy and casting method. The effects of various contents of AlN (0.5-3.0 wt.%) on the microstructure and mechanical properties of the Mg-4Al-4La-0.3Mn (AE44) alloy at room (25 °C) and high temperatures (150-250 °C) were investigated. Microstructure analysis revealed that the inclusion of AlN led to a reduction in both the grain size and second phase size in the AE44 alloy, while also improving the distribution of the second phase. The average grain size, Al11La3 phase, Al2La phase, and Al3La phase of the 2.0 wt.% AlN/AE44 composite were 135.7, 9.6, 1.9, and 12.6 μm, respectively, which were significantly lower than those of the AE44 matrix alloy (179.8, 12.6, 3.3, 17.8 μm). The refinement was attributed to the ability of AlN particles to serve as heterogeneous nucleation cores for α-Mg and, at the same time, impede the growth of the solid-liquid interface, eventually leading to grain refinement. With the increase in the AlN content, the mechanical properties of composites initially exhibited an increase at both room and high temperatures, followed by a subsequent decrease. When the AlN content was 2.0 wt.%, the composite exhibited optimal strength and plasticity matching. At room temperature, the TYS, UTS, and EL values of the 2.0 wt.% Mg-4Al-4La-0.3Mn composite were 96 MPa, 175 MPa, and 7.0%, respectively, which were increased by 26 MPa, 27 MPa, and 0.7% when compared with the base alloy. The TYS of the 2.0 wt.% Mg-4Al-4La-0.3Mn composite at 150 °C, 200 °C, and 250 °C were 17 MPa, 14 MPa, and 22 MPa higher than those of the matrix alloy, respectively. The main strengthening mechanisms were second phase strengthening, load transfer strengthening, and thermal mismatch strengthening. At elevated temperatures, AlN particles effectively pinned the grain boundaries, inhibiting their migration, and hindered dislocation climbing, resulting in excellent mechanical properties of the composites at high temperatures. This study contributes to the advancement of in situ AlN particle preparation methods and the exploration of effects of AlN on the properties and microstructure of Mg-Al-RE alloys at high temperatures (150-250 °C).

Processing of high-strength thermal-resistant Al-2.2% cerium-1.3% lanthanum alloy rods with high electric conductivity by High Pressure Torsion Extrusion

A novel severe plastic deformation (SPD) process of High Pressure Torsion Extrusion (HPTE) was applied to the rods of the Al-2.2 wt.% Ce-1.3 wt.% La (Al–3.5RE) alloy. The microstructure, microhardness, the mechanical strength, thermal stability, and electrical conductivity of the alloy after HPTE and subsequent annealing have been investigated. It was demonstrated that HPTE processing can simultaneously increase yield strength from 127 to 225 MPa and electrical conductivity from 54.7% IACS to 55.7% IACS in this alloy. Such a remarkable combination of properties was achieved thanks to significant refinement of microstructure constituents: grain size of Al matrix was reduced down to 0.9 µm and initially continuous network of Al11RE3 phase was broken to micrometer- and nanometer-sized particles. Furthermore, the yield strength of the HPTE-processed Al–3.5 RE alloy remains stable at 230 °C for 1 h due to micrometer- and nanometer-sized particles that pin the grain boundaries. Therefore, HPTE processing of Al–RE alloys has a high application potential in the electric power industry.Graphical abstract

Controllable reinforcement phase distribution at the grain scale via a simple precipitation process

Due to the inability of Zr to refine Al-containing Mg alloys, achieving pronounced grain refinement in cast AZ31 alloy has been a significant challenge for researchers. Surprisingly, we found that the reinforcement phases demonstrated a regular distribution at the grain scale after adding 0.9 wt% Nd and 0.3 wt% Y: Al2RE inside the grains and Al11RE3 agglomerated near the grain boundaries. Additionally, the grain size of AZ31 alloy was significantly reduced from 258 µm to 65 µm. The mechanisms of reinforcement phase distribution and grain refinement were explored through the combination of transmission electron microscope (TEM) and thermal analysis during the solidification process. Al2RE phase precipitates prior to α-Mg, and exhibits a specific orientation relationship with the matrix: 011̅0Mg∥011Al2RE，0002Mg∥22̅2Al2RE. This suggests that Al2RE serves as potentially effective heterogeneous nucleation sites for α-Mg. Moreover, Al11RE3 phase can restrict grain growth in the later stage of solidification. The tensile results show that a regular distribution of the reinforcement phase at the grain scale can not only effectively alleviate stress concentration, but suppress the formation of coarse twins by inducing grain refinement during alloy solidification process, significantly improving the strength and ductility of the alloy.

Influence of minor RE addition on microstructures, tensile properties, and creep resistance in a die-cast Mg–Al–Ca–Mn alloy

In this work, we have investigated the influence of RE content on the tensile property, creep resistance, and microstructures of a die-cast Mg–9Al-0.3Ca-0.2Mn (wt. %). Minor content of RE elements simultaneously increases the strength and ductility, which is mostly since RE addition refined primary dendritic α-Mg and eutectic α-Mg matrix and eutectic β-Mg17Al12 phases and formed thermally stable Al11RE3 phases. The 0.6% RE adding alloy obtains the best strength-ductility synergy along with the UTS of 245 MPa, TYS of 170 MPa, and EL of 5.7%. The 0.6−1.0% RE addition gives rise to a reduction of the minimum creep rate by over one order of magnitude of the alloy, indicating a significant enhancement in creep resistance, which can be mainly attributed to RE addition introducing Al11RE3 phases to prevent grain boundary sliding, and suppressing dynamic precipitation of γ-Mg17Al12 phases during high-temperature creep. These results can provide important references for the design of creep-resistant die-cast Mg alloys and promote the application of commercial Mg–Al based alloys at high temperatures.

Fracture-based modeling of heat-treated AZ91/AZE911 magnesium alloys for estimating high-cycle fatigue lifetime by Paris crack growth rate and striations spacing

In the present research, the fracture behavior of the AZ91 magnesium alloy is analyzed based on the striations spacing on the fracture surface for predicting the fatigue High-Cycle Fatigue lifetime. At first, equations and relations were extracted based on the Paris law. Then, striations spacing was measured using ImageJ software and field emission scanning electron microscope images of fracture surfaces of heat-treated Mg–Al–Zn alloys, containing and non-containing 1% rare earth elements (1% RE). Finally, constants of the Paris law were calculated and calibrated. Results showed that a 1% RE addition decreased the striations spacing and enhanced the fatigue resistance (between 14 and 40%). In addition, the lifetime scatter band and mean error decreased from ± 2.7X to ± 1.5X and from 150 to 33%, respectively, as the accuracy of the recommended model. Heat-treating transformed the continuous precipitations to blade-shaped precipitations on the Mg-matrix and decreased the grain size remarkably. The addition of 1% RE formed the new Al11RE3 phase and created a better distribution between the cast defects. In addition, fatigue striations in AZ91 alloy had more curvature and discontinuity and were more significant and coarser than those in AZE911 + 1% RE (AZE911) alloy.Graphical abstract

Effect of Solution Treatment Time on Microstructure Evolution and Properties of Mg-3Y-4Nd-2Al Alloy

In order to explore the microstructure evolution of an Mg-RE alloy refined by Al during solution treatment, an Mg-3Y-4Nd-2Al alloy was treated at 545 °C for different time periods. Phase evolution of the alloy was investigated. After solution treatment, the Mg-RE eutectic phase in the Mg-3Y-4Nd-2Al alloy dissolves, the granular Al2RE phase does not change, the acicular Al11RE3 phase breaks into the short rod-like Al2RE phase, and the lamellar Al2RE phase precipitates in the grains. With the extension of solution time, the precipitated phase of the lamellar Al2RE increased at first and then decreased, and its orientation relationship with the matrix is <112>Al2RE//<21¯1¯0>Mg and {111}Al2RE//{0002}Mg. The undissolved granular Al2RE phase can improve the thermal stability of the alloy grain by pinning the grain boundary, and the grain size did not change after solution treatment. Solution treatment significantly improved the plasticity of the alloy. After 48 h of solution treatment, the elongation increased to 17.5% from 8.5% in the as-cast state.

The microstructural features and strengthening mechanisms of Mg-Al-Zn-Ca-(RE) extruded alloys having high-volume fractions of second-phase particles

The microstructures and tensile properties of Mg-4∼6Al-2∼4Zn-2∼3Ca-0∼1RE (in wt.%) extruded alloys have been investigated. C15 and C36 Laves phases, Ca2Mg6Zn3, Al2REZn2, and Al11RE3 phases were formed as networks during solidification in different alloys. After extrusion, coarse dendritic were significantly refined due to dynamic recrystallization, second phases were fragmented into pieces arranged as stripes, and typical basal fiber texture {0002} <10-10> with the extrusive direction paralleled to (0001) were formed in all studied alloys. Laves phase particles were prone to be crushed into nanoparticles, which appeared more easily to hinder the recrystallized grain growth and could bring about more than 30 vol % ultra-fine grains after extrusion. During extrusion, twinning-induced dynamic recrystallization occurred at first, and both discontinuous and continuous dynamic recrystallization dominated the microstructural evolution. The volume fraction of second phases had critical roles in recrystallization process, and a nearly complete recrystallization degree could be obtained in alloys containing more than 9 vol% second phases. The strengthening mechanisms were evaluated based on classic strengthening models, which agreed well with the experimental results. It was found that grain boundary strengthening, second phase strengthening, and texture strengthening contributed around 60%, 30%, and 10%, respectively, to yield strengthening, except for Mg-4Al-4Zn-2Ca alloy because of the high percentage of unrecrystallized region. Moreover, the overestimate of second phase strengthening happened in alloys having more than 9 vol% second phases, which revealed that too many second phases had limited influence on microstructures and the resulting mechanical properties.

Microstructure and impact behavior of Mg-4Al-5RE-xGd cast magnesium alloys

This work investigated the microstructure and impact behavior of Mg-4Al-5RE-xGd (RE represents La-Ce mischmetal; x = 0, 0.2, 0.7 wt.%) alloys cast by high-pressure die casting (HPDC), permanent mold casting (PMC), and sand casting (SC) techniques. The results indicated that with increasing Gd content, the grain sizes of the HPDC alloy had a slight change, but the grains of the PMC and SC alloys were significantly refined. Besides, the acicular Al11RE3 phase was modified into the short-rod shape under the three casting conditions. The impact toughness of the studied alloy was mainly dominated by the absorbed energy during the crack initiation. With increasing Gd content, the impact toughness of the studied alloy monotonically increased due to the lower tendency of the modified second phase toward crack initiation. The impact stress was higher than the tensile stress, exhibiting a strain rate sensitivity for the mechanical response; however, the HPDC alloy had an inconsistent strain rate sensitivity during the impact event due to the transformation of the deformation mechanism from twinning to slip with increasing strain. Abundant dimples covered the fracture surface of the fine-grained HPDC alloys, indicating a typical ductile fracture. Nevertheless, due to the deficient {101¯2} twinning activity and the suppressed grain boundary sliding during the impact event, the HPDC alloys showed insufficient plastic deformation capacity.

Characteristics and formation mechanisms of defect bands in vacuum-assisted high-pressure die casting AE44 alloy

The microstructure in vacuum-assisted high-pressure die casting (HPDC) Mg-4Al-4RE (AE44) alloy was studied. Special attention was paid to the characteristics of defect bands and their formation mechanisms. Since double defect bands are commonly observed, the cross section of die cast samples is divided into five parts with different grain morphologies and size distributions. The inner defect band is much wider than the outer one. Both the defect bands are solute segregation bands, resulting in a higher area fraction of Al11RE3 phase than that in the adjacent regions. No obvious aggregation of porosities is observed in the defect bands of AE44 alloy. This may be due to a narrow solidification temperature range of AE44 alloy and a large amount of latent heat released during the precipitation of intermetallic phases. The formation of the defect bands is related to the shear stress acting upon the partially solidified alloy, which can lead to collapse of the grain network. However, the generation mechanisms of shear stress in the outer and inner defect bands are quite different.

The formation mechanism of Al-RE tubular phase in AZ80-Ce magnesium alloy by La doping

In this paper, the effect of La addition on the Al-RE phase in Mg-Al-Zn-Ce magnesium alloy was studied. Melting method was used to prepare AZ80-Ce magnesium alloys with different La content, and the morphological transformation mechanism of Al-RE phase was proposed by XRD, SEM, EPMA, TEM and extraction. The results show that the Al11RE3 phase can be formed by adding RE (Ce/La) into AZ80 magnesium alloy. With the increase of La, the morphology of Al11RE3 phase in the alloy changes from acicular to tubular. La replaces part of Ce in the Al11Ce3 cell and the Al11Ce3 phase is transformed into Al11RE3 phase based on Al11RE3 cell when La is added. In the Al11RE3 phase, the doping of La will cause lattice distortion in the crystal, which increases the surface energy on the growth surface of the Al11RE3 phase and accelerates its growth rate in (001) direction, resulting in the formation of tubular Al11RE3 phase. After forming the tubular structure, the growing process of Al11RE3 phase is divided into three stages owing to different control factors.

Defect band formation in high pressure die casting AE44 magnesium alloy

The characteristics of defect bands in the microstructure of high pressure die casting (HPDC) AE44 magnesium alloy were investigated. Special attention was paid to the effects of process parameters during the HPDC process and casting structure on the distribution of defect bands. Results show that the defect bands are solute segregation bands with the enrichment of Al, Ce and La elements, which are basically in the form of Al11RE3 phase. There is no obvious aggregation of porosities in the defect bands. The width of the inner defect band is 4–8 times larger than that of the outer one. The variation trends of the distribution of the inner and outer defect bands are not consistent under different process parameters and at different locations of castings. This is due to the discrepancy between the formation mechanisms of double defect bands. The filling and solidification behavior of the melt near the chilling layer is very complicated, which finally leads to a fluctuation of the width and location of the outer defect band. By affecting the content and aggregation degree of externally solidified crystals (ESCs) in the cross section of die castings, the process parameters and casting structure have a great influence on the distribution of the inner defect band.

Effects of Al addition on the microstructure, mechanical properties and thermal conductivity of high pressure die cast Mg–3RE–0.5Zn alloy ultrathin–walled component

Strength and heat dissipation capability are the key parameters for metal materials used as the structural components of 5G stations and smartphones, while balancing the high strength and high thermal conductivity is still a long-term challenge. In the present study, we attempted to achieve high–thermal–conductivity Mg alloys combined with high strength for high pressure die cast (HPDC) ultrathin-walled components. The effects of Al addition on the microstructure, tensile properties, thermal conductivity, and electrical conductivity of HPDC Mg–3RE–0.5Zn (wt%) alloy were investigated and discussed carefully. We found that the HPDC Mg–3RE–0.5Zn showed the highest thermal conductivity of 143.6 W(m·K)−1 and electrical conductivity of 18.9 MS·m−1. With the increasing Al addition, the thermal conductivity and electrical conductivity gradually decreased while still kept a high level of 126.1–117.8 W(m·K)−1 and 17.5–16.3 MS·m−1. Furthermore, Al addition simultaneously improved the strength and elongation of HPDC Mg–3RE–0.5Zn alloy, where the HPDC Mg–3RE–0.5Zn–2Al alloy exhibited the best tensile properties with yield strength, ultimate tensile strength, and elongation of 156 MPa, 240 MPa, and 10.8%, respectively. The Al addition modified the intermetallic phases from continuous networked Mg12RE to discontinuous blocky Al2RE and/or lamellar Al11RE3 phases, which contributed to enhancing tensile properties. The results will be helpful for developing high performance HPDC Mg alloys and extending their practical application.

Effect of Al Content on Microstructure Evolution and Mechanical Properties of As-Cast Mg-11Gd-2Y-1Zn Alloy.

In the present paper, the Mg-11Gd-2Y-1Zn alloys with different Al addition were fabricated by the gravity permanent mold method. The effect of Al content on microstructure evolution and mechanical properties of as-cast Mg-11Gd-2Y-1Zn alloy was studied by metallographic microscope, scanning electron microscope, XRD and tensile testing. The experimental results showed that the microstructure of as-cast Mg-11Gd-2Y-1Zn alloy consisted of α-Mg phase and island-shaped Mg3 (RE, Zn) phase. When Al element was added, Al2RE phase and lamellar Mg12REZn (LPSO) phase were formed in the Mg-11Gd-2Y-1Zn alloy. With increasing Al content, LPSO phase and Mg3 (RE, Zn) phase gradually decreased, while Al2RE phase gradually increased. There were only α-Mg and Al2RE phases in the Mg-11Gd-2Y-1Zn-5Al alloy. With the increase of Al content, the grain size decreased firstly and then increased. When the Al content was 1 wt.%, the grain size of the alloy was the minimum value (28.9 μm). The ultimate tensile strength and elongation increased firstly and then decreased with increasing Al addition. And the fracture mode changed from intergranular fracture to transgranular fracture with increasing addition. When Al addition was 1 wt.%, the maximum ultimate tensile strength reached 225.6 MPa, and the elongation was 7.8%. When the content of Al element was 3 wt.%, the maximum elongation reached 10.2% and the ultimate tensile strength was 207.7 MPa.

Creep properties and microstructure of a Mg-6Al-1Nd-1.5Gd alloy at temperatures above 150 °C

Compressive creep behavior of a Mg-Al alloy containing a small amount of Nd and Gd (Mg-6Al-1Nd-1.5Gd) was investigated at temperatures from 150 °C to 200 °C under a constant applied stress of 90 MPa, and its microstructure before and after creep testing was compared. Results showed that steady-state creep rate of the alloy was only 1.946 × 10−8 /s at 150 °C, and was increased by four times and almost one order of magnitude at 175 °C and 200 °C, respectively. The microstructure of the alloy mainly consists of α-Mg, β-Mg17Al12 phases, and Al2RE phases, which were distributed both in dendrites of α-Mg and at grain boundaries originally. After creep for 120 h, more Al2RE phases were aggregated at grain boundaries. The continuous β-Mg17Al12 phase turned into dispersed dot-like or blocky particles. As the test temperature increased, the number of dislocation lines gradually increased due to the increase of creep strain. Meanwhile, dislocation tangle and dislocation pile-ups occurred near grain boundaries. However, obvious slip traces and slip lines appeared inside α-Mg dendrites at 175 °C and 200 °C, respectively, indicating that 〈c + a〉 non-basal slip system was activated, creep resistance decreased dramatically.

Crystal structure, phase content, and tensile properties of As-cast Mg–Gd–Y–Al alloys

The lattice parameters, phase content, and tensile properties of as-cast Mg–xGd–(4–x)Y–2Al (x = 0, 2, 4) alloys were investigated via X-ray diffraction, Rietveld refinement, scanning electron microscopy, and transmission electron microscopy. The Mg-RE phase, Al2RE phase, and Al11RE3 phase occurred in all three alloys. Furthermore, the cell volume and axial ratio (c/a) of the α-Mg matrix decreased with increasing (0–4 wt.%) Gd content. The abundance of the Al2RE and Mg-RE phases decreased with increasing Gd content, whereas that of the Al11RE3 phase increased. Moreover, Al2RE particles formed at the grain centers served as active nucleation sites, thereby leading to grain refinement, and acicular Al11RE3 phases restricted the growth of α-Mg. The tensile properties improved with increasing Gd content. In fact, the optimal mechanical properties (yield strength: 77.83 MPa, ultimate tensile strength: 195.01 MPa, and elongation: 15.71 %) were obtained for the Mg–4Gd–2Al alloy. Furthermore, strengthening of the material occurred mainly via second-phase strengthening and solid-solution strengthening. Block Al2RE particles can cut the matrix during the stretching process, and the acicular Al11RE3 phase may play a major role in enhancing the tensile properties. In addition, the ductility of the alloy system improved with decreasing axial ratio (c/a).

Effects of heat treatment on the microstructural evolution and creep resistance of Elektron21 alloy and its nanocomposite

In previously published research, creep resistance of commercial alloy Elektron21 (El21) and El21 + 1% AlN/Al nanocomposite were predominantly investigated in as-cast condition, little work focused on creep resistance following heat treatment. In this work, El21 and its nanocomposite with and without T6 treatment (520 °C for 8 h and 200 °C for 16 h) were prepared to reveal the influence of heat treatment on their microstructural evolutions and creep properties. Different intermetallic particles and precipitates that formed in El21 and El21 + 1% AlN/Al with different states were characterized using optical microscopy (OM), X-ray diffraction (XRD), scanning electron microscope (SEM) and transmission electron microscopy (TEM). Creep tests were performed over a stress range of 80–140 MPa at 240 °C. Creep results showed that the application of T6 treatment could improve the creep resistance of El21, but deteriorate that of El21 + 1% AlN/Al. This is attributed to the reduced amount of γ'' and β′ precipitates in El21 + 1% AlN/Al (T6) after ageing, resulting from the formation of plate-like Al2(Nd, Gd) (Al2RE) precipitates. It is also found that after T6 heat treatment, El21 (T6) had a lower minimum creep rate with a shorter duration of secondary creep stage than El21 + 1% AlN/Al (T6) at high creep temperatures due to the overageing of precipitates and the thermal stability of the Al2RE particles. El21 + 1% AlN/Al nanocomposites, either in the as-cast or T6 condition, show a much longer duration of secondary creep than NP-free El21. The responsible mechanism was attributed to the addition of AlN NPs and the formation of particulate/plate Al2RE phase.

Effect of La/Nd ratio on microstructure and mechanical properties of as-cast AZ91-xLa/Nd alloy

The effect of La/Nd ratio on microstructure and mechanical properties of as-cast AZ91D alloys were investigated. The alloys were produced by casting the molten metal into a preheated steel mould. Microstructures were investigated by XRD and SEM (equipped with EDS). The hardness measurement was carried out by Brinell hardness (HB) digital display tester. Compression tests were conducted at both room and high temperatures (20 °C and 150 °C). Microstructural characterizations reveal that the area fraction of the β-Mg17Al12 phase changed with the variation of La/Nd ratio. The area fraction of the β-Mg17Al12 phase decrease significantly and then increased slightly with the increase of La/Nd ratio. Besides, the results show that the addition of La and Nd contributed to the formation of needle-like phase Al11RE3. Meanwhile, the Brinell hardness and high-temperature compression properties of this alloy reach the maximum values (67 HB and 330 MPa, respectively) when the La/Nd ratio is 2/3. In this alloy, the amount of Al11RE3 phase is 51/TA and the average length is 69.55 μm. Moreover, a generation model of Al11RE3 is established and the growth mechanism of Al11RE3 is analyzed. This work thus has proved that La/Nd ratio has a great effect on the microstructure and mechanical properties of AZ91.

Microstructure and Mechanical Properties of the Al-RE Alloy with Ca Addition.

Aluminum and its alloys are used in a wide range of industrial applications from low density, high strength and a variety of structural materials. In this study, the effects of Ca addition on the microstructure and mechanical properties of Al-1wt.%RE alloys were investigated. The melt was held at 800 °C for 20 minutes and poured into a mold. The cast Al alloy was hot extruded with a rod having a diameter of 12 mm and a reduction ratio of 38:1. Al-1wt.%RE alloy consists of Al, Al11RE₃ phase. The Al₂Ca phase is increased by increasing the Ca content to 0.2 to 0.4 wt.%. As the Ca content increased from 0 to 0.4 wt.%, the average grain size of the extruded Al alloy decreased by 739.8, 400.8 and 155.0 μm. The tensile strengths were increased to 74.25, 76.53, and 79.52 MPa. The electrical conductivity of Al-RE alloy with Ca addition decreased to 60.32, 58.15 and 57.89% IACS.