The rate of formation of intermetallic layers between aluminum and steel below 660°C

The rate of formation of intermetallic compounds between aluminum and three ferritic steels, one austenitic steel, and Inconel has been determined by an electrolytic method. The steel was held at zero potential with respect to aluminum in a NaCl-AlCl₃ melt, and the current measured. Comparison of measured thicknesses of intermetallic layers with those calculated from the integrated current gives an average deposition efficiency of 95 pct. For the Type 304 austenitic steel thickness (min), andk is given by logk= −6400/T(⁰K) +4.469. The ferritic steels show a linear rate of growth of Al₅Fe₂, with an initial higher rate such that extrapolation of the linear curve back to zero time gives an intercept of 16±7 μm. The rate constants (mm min⁻¹) may be represented by log (rate)=α/T+β, and the values of α and β are respectively −2650 and−0.788 for a plain carbon steel,−6580 and + 3.469 for a 1.3 pct Cr, 0.4 pct Mo steel, and−5950 and +2.466 for a 2.2 pct Cr, 0.9 pct Mo steel. The more highly alloyed steels are thus attacked, more slowly. Results for Inconel could not be fitted to any simple equation. With the ferritic steels growth is by aluminum diffusing inwards; with Inconel it is by nickel diffusing outward.     

A Novel Bonding Method of Pure Aluminum and SUS304 Stainless Steel Using Barrel Nitriding

A great deal of research is being carried out on welding or bonding methods between iron and aluminum. However, it is not so easy to make Fe-Al bonding materials with both high strength and light weight. Recently, a new nitriding process has been proposed to produce aluminum nitride on an aluminum surface using a barrel. This study proposes a new concept in the production of a multilayer which has an AlN and Fe-Al intermetallic compound layer between the aluminum and steel using a barrel nitriding process. The bonding process was carried out from 893 K to 913 K (620 °C to 640 °C) for 18, 25.2, and 36 ks with Al₂O₃ powder and Al-Mg alloy powder. After the process, an aluminum nitride (AlN) layer and a Fe-Al intermetallic compound (Fe₂Al_5.4) layer were formed at the interface between the pure aluminum and SUS304 austenitic stainless steel. The thicknesses of the AlN layer and the intermetallic compound layer increased with increasing treatment temperature and time. The maximum hardnesses of the AlN layer and Fe₂Al_5.4 layers were found to be 377HV and 910HV, respectively, after barrel nitriding at 893 K (620 °C) for 18 ks.     

Diffusion Bonding of 17-4 Precipitation Hardening Stainless Steel to Ti Alloy With and Without Ni Alloy Interlayer: Interface Microstructure and Mechanical Properties

In the present study, the diffusion bonding of 17-4 precipitation hardening stainless steel to Ti alloy with and without nickel alloy as intermediate material was carried out in the temperature range of 1073 K to 1223 K (800 °C to 950 °C) in steps of 298 K (25 °C) for 60 minutes in vacuum. The effects of bonding temperature on interfaces microstructures of bonded joint were analyzed by light optical and scanning electron microscopy. In the case of directly bonded stainless steel and titanium alloy, the layerwise α-Fe + χ, χ, FeTi + λ, FeTi + β-Ti phase, and phase mixture were observed at the bond interface. However, when nickel alloy was used as an interlayer, the interfaces indicate that Ni₃Ti, NiTi, and NiTi₂ are formed at the nickel alloy-titanium alloy interface and the PHSS-nickel alloy interface is free from intermetallics up to 1148 K (875 °C) and above this temperature, intermetallics were formed. The irregular-shaped particles of Fe₅Cr₃₅Ni₄₀Ti₁₅ have been observed within the Ni₃Ti intermetallic layer. The joint tensile and shear strength were measured; a maximum tensile strength of ~477 MPa and shear strength of ~356.9 MPa along with ~4.2 pct elongation were obtained for the direct bonded joint when processed at 1173 K (900 °C). However, when nickel base alloy was used as an interlayer in the same materials at the bonding temperature of 1148 K (875 °C), the bond tensile and shear strengths increase to ~523.6 and ~389.6 MPa, respectively, along with 6.2 pct elongation.     

The Effect of Cu Powder During Friction Stir Welding on Microstructure and Mechanical Properties of AA3003-H18

Friction stir welding (FSW) was used to join 3003-H18 non-heat-treatable aluminum alloy plates by adding copper powder. The copper powder was first added to the gap (0.1 and 0.2 mm) between two plates and then the FSW was performed. The specimens were joined at various rotational speeds of 800, 1000, and 1200 rpm at traveling speeds of 70 and 100 mm/min. The effects of rotational speed, second pass of FSW, and direction of second pass also were studied on copper particle distribution and formation of Al-Cu intermetallic compounds in the stir zone. The second pass of FSW was carried out in two ways; in line with the first pass direction (2F) and in the reverse direction of the first pass (FB). The microstructure, mechanical properties, and formation of intermetallic compounds type were investigated. In high copper powder compaction into the gap, large clusters were formed in the stir zone, while fine clusters and sound copper particles distribution were obtained in low powder compaction. The copper particle distribution and amount of Al-Cu intermetallic compounds were increased in the stir zone with increasing the rotational speed and applying the second pass. Al₂Cu and AlCu intermetallic phases were formed in the stir zone and consequently the hardness was significantly increased. The copper particles and in situ intermetallic compounds were symmetrically distributed in both advancing and retreating sides of weld zone after FB passes. Thus, the wider area was reinforced by the intermetallic compounds. Also, the tensile test specimens tend to fracture from the coarse copper aggregation at the low rotational speeds. At high rotational speeds, the fracture locations are placed in HAZ and TMAZ.     

Microstructural Evolution of the 55 Wt Pct Al-Zn Coating During Press Hardening

Press hardening is increasingly being used to produce ultra-high strength steel parts for passenger cars. Al-Si, Zn, and Zn-alloy coatings have been used to provide corrosion protection to press hardening steel grades. The use of coatings has drawbacks such as coating delamination or liquid metal-induced embrittlement. In the present work, the microstructural evolution of Al-Zn coating during press hardening was studied. The 55 wt pct Al-Zn coating can in principle provide both Al barrier protection and Zn cathodic protection to press hardened steel. During the heat treatment associated with the press hardening, the 55 wt pct Al-Zn alloy coating is converted to an intermetallic surface layer of Fe₂Al₅ and a FeAl intermetallic diffusion layer. The Zn is separated from both intermetallic compounds and accumulates at grain boundaries and at the surface. This Zn separation process is beneficial in terms of providing cathodic protection to Al-Zn coated press hardening steel.     

Investigation on Metallurgical Structure and Mechanical Properties of Dissimilar Al 2024/Cu FSW T-joints

In this research, T-joining of AA2024-T4 and commercially pure copper were performed successfully using friction stir welding. Effect of welding parameters on metallurgical and mechanical characteristics of the joints was studied. For this purpose, tensile strength, microhardness, and macro- and microstructures of the joints were investigated. Also, the fracture surfaces were examined using XRD and SEM. The best results were obtained for the 1130 rpm rotation speed (ω) and 12 mm/min travel speed (v), with the UTS of 156 MPa (~70% of Cu strength). The microhardness test showed that TMAZ and base metal of Al side had the maximum hardness amounts (148 and 155 HV, respectively). Generally, increase in the ω²/v ratio caused the nugget zone and HAZ grain size to increase. The results revealed the formation of Al₂Cu and Al₄Cu₉ intermetallic compounds in the border zone of the joints. The fractography results showed the occurrence of cleavage fracture in all the samples.     

Microstructural Characterization and Properties Evaluation of Ni-Based Hardfaced Coating on AISI 304 Stainless Steel by High Velocity Oxyfuel Coating Technique

The present study concerns a detailed investigation of microstructural evolution of nickel based hardfaced coating on AISI 304 stainless steel by high velocity oxy-fuel (HVOF) deposition technique. The work has also been extended to study the effect of coating on microhardness, wear resistance and corrosion resistance of the surface. Deposition has been conducted on sand blasted AISI 304 stainless steel by HVOF spraying technique using nickel (Ni)-based alloy [Ni: 68.4 wt pct, chromium (Cr): 17 wt pct, boron (B): 3.9 wt pct, silicon (Si): 4.9 wt pct and iron (Fe): 5.8 wt pct] of particle size 45 to 60 ??m as precursor powder. Under the optimum process parameters, deposition leads to development of nano-borides (of chromium, Cr₂B and nickel, Ni₃B) dispersion in metastable and partly amorphous gamma nickel (??-Ni) matrix. The microhardness of the coating was significantly enhanced to 935 VHN as compared to 215 VHN of as-received substrate due to dispersion of nano-borides in grain refined and partly amorphous nickel matrix. Wear resistance property under fretting wear condition against WC indenter was improved in as-deposited layer (wear rate of 4.65 × 10^?7 mm³/mm) as compared to as-received substrate (wear rate of 20.81 × 10^?7 mm³/mm). The corrosion resistance property in a 3.56 wt pct NaCl solution was also improved.     

Intermetallic phases formed during hot dipping of

The formation and growth of intermetallic phases during hot dipping of low carbon steel in a Galfan bath (5 wt pct Al-Zn plus 0.05 pct mischmetal) at 450 °C have been studied by using scanning electron microscopy, X-ray diffraction, and energy dispersive spectroscopy (EDS). The first intermetallic phase to appear was in the form of local outbursts at the substrate/melt interface; intermetallic phases subsequently developed a breakaway morphology. Both the inter- metallic outbursts and the breakaway were found to be mixtures of Fe₂Al₅-Zn_x and FeAl₃-Zn_x, the latter being in each case further away from the intermetallic/substrate interface. The initial outbursts were determined to be mainly Fe₂Al₅-Zn_x; this phase grew into the substrate with a (001) preferred growth direction. The breakaway was mainly FeAl₃-Zn_x with Fe₂Al₅-Zn_x found only close to the interface. Both intermetallic growth morphologies can be characterized by a reaction path of Fe (substrate)/Fe₂Al₅-Zn_x/FeAl₃-Zn_x/galfan (melt).     

Microstructures and Tensile Properties of Hot-Extruded Al Matrix Composites Containing Different Amounts of Al4Sr

In this investigation, the effect of hot extrusion process has been studied on the microstructure and tensile properties of aluminum matrix composite containing different amounts (10, 15, and 20 wt pct) of Al₄Sr intermetallic phase. Microstructural examinations assessed by scanning electron microscopy revealed that hot extrusion breaks large Al₄Sr particles and reduces their length tremendously. It was also found that although the addition of Al₄Sr content in the composite reduces ultimate tensile strength and elongation values, hot extrusion improves tensile results significantly. Remarkable result of this study was concerned with significant improvement in the toughness of hot-extruded Al-10 wt pct Al₄Sr composite in which elongation values raised up to 22 pct. Therefore, optimum amount of Al₄Sr intermetallic in the composite was found to be 10 wt pct. Fractographic examinations revealed that hot extrusion encourages ductile mode of fracture by introducing homogeneous distribution of fine dimples on the fracture surface of the composites.     

Microbial Beneficiation of Salem Iron Ore Using Penicillium purpurogenum

High alumina and silica content in the iron ore affects coke rate, reducibility, and productivity in a blast furnace. Iron ore is being beneficiated all around the world to meet the quality requirement of iron and steel industries. Choosing a beneficiation treatment depends on the nature of the gangue present and its association with the ore structure. The advanced physicochemical methods used for the beneficiation of iron ore are generally unfriendly to the environment. Biobeneficiation is considered to be ecofriendly, promising, and revolutionary solutions to these problems. A characterization study of Salem iron ore indicates that the major iron-bearing minerals are hematite, magnetite, and goethite. Samples on average contains (pct) Fe₂O₃-84.40, Fe (total)-59.02, Al₂O₃-7.18, and SiO₂-7.53. Penicillium purpurogenum (MTCC 7356) was used for the experiment. It removed 35.22 pct alumina and 39.41 pct silica in 30 days in a shake flask at 10 pct pulp density, 308 K (35 °C), and 150 rpm. In a bioreactor experiment at 2 kg scale using the same organism, it removed 23.33 pct alumina and 30.54 pct silica in 30 days at 300 rpm agitation and 2 to 3 l/min aeration. Alumina and silica dissolution follow the shrinking core model for both shake flask and bioreactor experiments.     

Characterization of Joints Between Aluminum and Galvanized Steel Sheets

Sound joints between an AA6016 aluminum sheet of 1.2-mm thickness and a low-carbon galvanized steel sheet of 0.77-mm thickness are obtained using the laser pseudo-brazing method. A zinc-based aluminum alloy is used as a filler wire with optimized process parameters for laser pseudo-brazing. Metallurgical investigation of the joint is carried out using a scanning electron microscope and energy-dispersive X-ray analysis. Joints produced using Al-Zn filler wire showed a moderate strength and quality with a layer containing principally Fe₂Al₅Zn _x type intermetallics of ~10-μm thickness. Failure in the heat-affected zone of aluminum is found to be dominative, while in some cases, fracture along the interface between the intermetallic layer and the steel sheet is observed.     

Effect of Partial Substitution of Mn for Ni on Mechanical Properties of Friction Stir Processed Hypoeutectic Al-Ni Alloys

In this study, the mechanical properties of as-cast and FSPed Al-2Ni-xMn alloys (x?=?1, 2, and 4 wt pct) were investigated and compared with those of the as-cast and FSPed Al-4Ni alloy. According to the results, the substitution of 2 wt pct Mn for 2 wt pct Ni leads to the formation of fine Mn-rich intermetallics in the microstructure increasing the tensile strength, microhardness, fracture toughness, and specific strength of alloy by 22, 56, 45, and 35 pct, respectively. At higher Mn concentrations, the formation of large Mn-rich platelets in the microstructure reduces the tensile properties. Friction stir processing at 12 mm/min and 1600 rpm significantly enhances both the strength and ductility of the alloy. The tensile strength, yield strength, fracture strain, fracture toughness, microhardness, and specific strength of FSPed Al-2Ni-4Mn alloy improved by 97, 83, 30, 380, 152, and 110  pct, respectively, as compared to those of the as-cast Al-4Ni alloy. This can be attributed to dispersion strengthening of Ni- and Mn-rich dispersoids, formation of ultrafine grains, and elimination of casting defects. The fractography results also show that the brittle fracture mode of the as-cast Mn-rich alloys turns to a more ductile mode, comprising fine and equiaxed dimples in FSPed samples.     

Effect of Nd Additions on Extrusion Texture Development and on Slip Activity in a Mg-Mn Alloy

Two Mg-1 wt pct Mn alloys containing 0.5 wt pct and 1 wt pct Nd have been processed by indirect extrusion at temperatures ranging from 548 K (275 °C) to 633 K (360 °C) and speeds between 2.8 and 11 mm/s. The microstructure and the texture of the extruded bars were analyzed in order to understand the effect of the processing parameters and of the rare-earth (RE) alloying additions on the texture development. Increasing the Nd content results in weak textures in which the predominant orientations are a function of the extrusion conditions. This may be explained by the occurrence of particle pinning of grain boundaries and by the nucleation of grains with a wider range of orientations. Mechanical tests were carried out in tension and in compression in all the processed samples at 10^?3 s^?1 and room temperature. It was found that larger RE amounts give rise to the disappearance of the yield asymmetry and to an anomalously high activity of tensile twinning, especially at the lowest extrusion temperatures. This has been attributed to an increase of the critical resolved shear stress of basal slip due to the presence of Mg₃Nd coherent and semi-coherent intermetallic prismatic plates.     

Effect of Cooling Rate and Neodymium Addition on Beta Intermetallic Phase of Al–Fe–Si Ternary System

Aluminium silicon alloys are widely used in automotive industry and other structural application. However, the presence of high content of iron element in Al–Si alloys lead to precipitation of beta intermetallic phase that has a detrimental effect on mechanical properties. Reducing the adverse effects of β-Al₉Fe₂Si₂ precipitates can be achieved by altering their morphology by adding element modifier and increasing solidification cooling rate. In this present work, simultaneous thermal analysis was used to study the effect of cooling rate (5, 10 and 30 °C min^?1) on beta phase formation in Al–7Si–1Fe alloy added with neodymium at 0.3, 0.6 and 1 wt%. The beta phase precipitates were then characterized using optical microscopy and scanning electron microscopy equipped with EDS. Image analysis results showed the reduction in size of beta intermetallic phase as a result of the rare earth addition. Further analysis also showed the refinement of eutectic silicon.     

Strength and toughness of Fe-10ni alloys containing C,Cr, Mo,and Co

The effects of C (0.10 to 0.20 pct), Cr (0 to 3 pct), Mo (0 to 2 pct), and Co (0 to 8 pct) on the yield strength, toughness (Charpy shelf energy), and tempering behavior of martensitic lONiCr-Mo-Co steels have been investigated. Variations in the carbon content between 0.10 and 0.20 pct result in yield strengths between 160 and 210 ksi (1.1 and 1.45 GN/m²) when these steels are tempered at 900° to 1000°F (480° to 540°C) for times of 1 to 100 h. These steels exhibit a secondary-hardening peak at 900° to 1000° F (480° to 540°C) where coarse Fe₃C carbides are gradually replaced by a fine, dislocation-nucleated dispersion of (Mo, Cr)₂C carbides. Maximum toughness at a given yield strength in these steels is only obtained when they are tempered for sufficiently long times so that the coarse Fe₃C carbides are completely dissolved. Molybdenum is primarily responsible for the secondary-hardening peak observed in these steels. However, chromium additions do result in lower secondaryhardening temperatures and promote coarsening of the secondary-hardening carbide. Best combinations of strength and toughness are obtained with steels containing 2 pct Cr and 1 pct Mo. Cobalt increases the yield strength of these steels over the entire tempering range and results in a higher secondary-hardening peak. This effect of cobalt is attributed to 1) a retardation in the rate of recovery of the dislocation substructure of the martensite, 2) the formation of a finer dispersion of secondary-hardening carbides, and 3) solid-solution strengthening. The finer dispersion of secondary-hardening carbides in steels containing cobalt is favored by the finer dislocation substructure in these steels since the (Mo, Cr)₂C carbide is dislocation-nucleated. This fine dispersion of (Mo, Cr)₂C carbide combined with the high nickel content accounts for the excellent combination of strength and toughness exhibited by these steels.     

The Effect of Cooling Rate from Solution on the Lattice Misfit During Isothermal Aging of a Ni-Base Superalloy

The evolution of lattice misfit in the polycrystalline nickel-base superalloy, RR1000, has been investigated using high resolution neutron diffraction at interrupted time intervals during an aging heat treatment. Samples were subjected to a super-solvus heat treatment followed by either a 100 or a 1 K min^?1 cooling rate prior to aging. Irrespective of cooling rate, the lattice misfit remained unchanged at approximately 0.1 pct throughout the aging cycle, indicating the microstructure remained stable. Microstructural observations validated this result for samples cooled at 1 K min^?1. However, for the faster, 100 K min^?1, cooling rate, whilst the secondary γ′ remained unchanged, the tertiary γ′ showed significant coarsening. Simulated diffraction patterns were used to investigate the influence of volume fraction, particle size, and lattice parameter of individual γ′ distributions on the measured lattice misfit. The results obtained indicate that conventional methods of measuring lattice misfit will be dominated by the γ′ distribution with the highest volume fraction, and may therefore obscure subtle changes in the γ′ distributions with lower a volume fraction.     

Effect of Bonding Time on Interfacial Reaction and Mechanical Properties of Diffusion-Bonded Joint Between Ti-6Al-4V and 304 Stainless Steel Using Nickel as an Intermediate Material

In the current study, solid-state diffusion bonding between Ti-6Al-4V (TiA) and 304 stainless steel (SS) using pure nickel (Ni) of 200-μm thickness as an intermediate material was carried out in vacuum. Uniaxial compressive pressure and temperature were kept at 4 MPa and 1023 K (750 °C), respectively, and the bonding time was varied from 30 to 120 minutes in steps of 15 minutes. Scanning electron microscopy images, in backscattered electron mode, revealed the layerwise Ti-Ni-based intermetallics like either Ni₃Ti or both Ni₃Ti and NiTi at titanium alloy-nickel (TiA/Ni) interface, whereas nickel-stainless steel (Ni/SS) interface was free from intermetallic phases for all the joints. Chemical composition of the reaction layers was determined by energy dispersive spectroscopy (SEM–EDS) and confirmed by X-ray diffraction study. Maximum tensile strength of ~382 MPa along with ~3.7 pct ductility was observed for the joints processed for 60 minutes. It was found that the extent of diffusion zone at Ni/SS interface was greater than that of TiA/Ni interface. From the microhardness profile, fractured surfaces, and fracture path, it was demonstrated that the failure of the joints was initiated and propagated apparently at TiA/Ni interface near Ni₃Ti intermetallic for bonding time less than 90 minutes, and through Ni for bonding time 90 minutes and greater.     

Role of Tungsten in the Tempered Martensite Embrittlement of a Modified 9 Pct Cr Steel

The effect of tempering on the mechanical properties and fracture behavior of two 3 pct Co-modified 9 pct Cr steels with 2 and 3 wt pct W was examined. Both steels were ductile in tension tests and tough under impact tests in high-temperature tempered conditions. At T ≤ 923 K (650 °C), the addition of 1 wt pct W led to low toughness and pronounced embrittlement. The 9Cr2W steel was tough after low-temperature tempering up to 723 K (450 °C). At 798 K (525 °C), the decomposition of retained austenite induced the formation of discontinuous and continuous films of M₂₃C₆ carbides along boundaries in the 9Cr2W and the 9Cr3W steels, respectively, which led to tempered martensite embrittlement (TME). In the 9Cr2W steel, the discontinuous boundary films played a role of crack initiation sites, and the absorption energy was 24 J cm^?2. In the 9Cr3W steel, continuous films provided a fracture path along the boundaries of prior austenite grains (PAG) and interlath boundaries in addition that caused the drop of impact energy to 6 J cm^?2. Tempering at 1023 K (750 °C) completely eliminated TME by spheroidization and the growth of M₂₃C₆ carbides, and both steels exhibited high values of adsorbed energy of ≥230 J cm^?2. The addition of 1 wt pct W extended the temperature domain of TME up to 923 K (650 °C) through the formation of W segregations at boundaries that hindered the spheroidization of M₂₃C₆ carbides.     

Oxygen Permeation of Partly Molten Slags

The conductivities, oxygen ion transference numbers, and oxygen permeation fluxes of NiO-30, 36, 42, and 48 wt pct Bi₂O₃, In₂O₃-30, 36, 42, and 48 wt pct Bi₂O₃, ZnO-15, 20, 25, and 30 wt pct Bi₂O₃, ZrV₂O₇-16, 20, 24, and 28 wt pct V₂O₅, and BiVO₄-5, 7, 10, and 12 wt pct V₂O₅ partly molten slags have been measured by using the four-probe DC, volumetric measurements of the faradaic efficiency, and gas flow techniques, respectively, under various temperatures and oxygen partial pressure gradients. Results indicate that in the ranges of slag layer thicknesses 1 to 5 mm and temperatures 923 K to 1173 K (650 °C to 900 °C), used in the present study, the overall oxygen permeation kinetics is controlled by both chemical diffusion and surface exchange reactions. The oxygen permeation fluxes (3 × 10^?9 to 9 × 10^?8 mol/cm² s) were found to increase with volume fraction of liquid. The oxygen ion transference number was found to be in the range 0.2 to 0.8. The ambipolar conductivity, characteristic thickness, and surface exchange coefficient were estimated to be in the ranges 1.1 × 10^?3 to 2.3 × 10^?1 S/cm, 2 × 10^?2 to 7 × 10^?2 cm, and 1.3 × 10^?6 to 2.1 × 10^?6 cm/s, respectively.     

A Comprehensive Study of Diffusion Bonding of Mg AZ31 to Al 5754, Al 6061 and Al 7039 Alloys

In the present study, microstructural and mechanical properties of diffusion bonding of AZ31–Mg with Al 5754, Al 6061, and Al 7039 alloys were compared under same conditions. The vacuum diffusion processes were performed at a temperature of 440 °C, the pressure of 29 MPa, and a vacuum of 1?×?10^?4 torr for 60 min. The microstructural characterizations were investigated using optical microscopy and scanning electron microscopy equipped with EDS analysis and linear scanner. The XRD analysis was performed to study phase figures near the interface zone. The results revealed the formation of brittle intermetallic compounds like Al₁₂Mg₁₇, Al₃Mg₂, and their other combinations at bonding interfaces of all samples. Additionally, the hardness of Al alloys seemed to play a key role in increasing diffusion rate of magnesium atoms toward the aluminum atoms, with Al 6061 alloy having the highest diffusion rate. It consequently led to an increase in diffusion rate and thus formation of a strong diffusion bonding between magnesium and aluminum alloys. The highest strength was about 42 MPa for the diffusion bonding between Mg AZ31 and Al 6061. Further investigations on surfaces indicated that the brittle phases especially Al₃Mg₂ caused brittle fracturing.