Microstructure Characteristics and Mechanical Properties of Al 413/Mg Joint in Compound Casting Process

Al 413/Mg couples were prepared by the compound casting process. Characterization of the interface by an optical microscope and scanning electron microscope (SEM) showed that a relatively uniform interface composed of three different layers is formed at the interface. The thickness of the interface depended on the melt/insert volume ratio (VR) significantly and was 80?and 470? ??m? in 1.25?and 3?VRs, respectively. The results of the energy dispersive X-ray spectroscopy (EDS), wavelength dispersive X-ray spectroscopy (WDS), and X-ray diffraction analysis showed that the interface layers are mainly composed of Al₃Mg₂, Al₁₂Mg₁₇, and Mg₂Si intermetallic compounds. An accumulation of magnesium oxide films was detected within the (Al₁₂Mg₁₇?+???) eutectic structure of the interface next to the magnesium base metal. Despite different thicknesses of the interface, shear strengths of the Al 413/Mg couples prepared in 1.25?and 3?VRs were almost same. The study of the fracture surfaces of the Al 413/Mg couples revealed that the accumulated magnesium oxide films act as a weak point for initiation of longitudinal cracks and failure of the joint.     

Diffusion Brazing of Al6061/15 Vol. Pct Al2O3p Using a Cu-Sn Interlayer

Diffusion brazing of Al-6061 alloy containing 15 vol. pct Al₂O₃ particles was attempted using Cu-Sn interlayer. Joint formation was attributed to the solid-state interdiffusion of Cu and Sn followed by eutectic formation and subsequent isothermal solidification. Examination of the joint region using scanning electron microprobe analyzer (EPMA), wavelength dispersive spectroscopy (WDS) and X-ray diffraction (XRD) showed the formation of intermetallic phases such as Al₇Cu₃Mg₃, Mg₂Cu₆Al₅, Cu₃Sn, and Mg₂Sn. The results indicated an increase in joint strength with increasing bonding time giving the highest joint shear strength of 94 MPa at a bonding duration of 3 hours.     

Microstructure and phase constituents in the interface zone of Mg/Al diffusion bonding

The microstructure and phase constituent for the Mg/Al diffusion-bonded joint were studied via scanning electron microscope (SEM), microhardness test, electron probe microanalyzer (EPMA), and X-ray diffraction (XRD). The test results indicated that the new compact phase was formed near the transition region of the Mg/Al diffusion interface. There are three new phase layers in the transition region. The microhardness of the diffusion zone is higher than that of the Mg and Al substrate. The fracture morphology mainly consists of a coarse and gray fracture, and the fracture is mainly the mixed fracture of cleavage and intergranular. X-ray diffraction tests indicate that the diffusion zone of the Mg/Al diffusion-bonded joint consists of intermetallic compounds MgAl, Mg₃Al₂, and Mg₂Al₃. With the increase of temperature, the content of Mg₃Al₂ and Mg₂Al₃ phases with good stability was increased.     

Analysis of Nugget Formation During Resistance Spot Welding on Dissimilar Metal Sheets of Aluminum and Magnesium Alloys

The nugget formation of resistance spot welding (RSW) on dissimilar material sheets of aluminum and magnesium alloys was studied, and the element distribution, microstructure, and microhardness distribution near the joint interface were analyzed. It was found that the staggered high regions at the contact interface of aluminum and magnesium alloy sheets, where the dissimilar metal melted together, tended to be the preferred nucleation regions of nugget. The main technical problem of RSW on dissimilar metal sheets of aluminum and magnesium alloys was the brittle-hard Al₁₂Mg₁₇ intermetallic compounds distributed in the nugget, with hardness much higher than either side of the base materials. Microcracks tended to generate at the interface of the nugget and base materials, which affected weld quality and strength.     

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.     

Influence of silicon on the wetting-bond strength-structure relationship in the AlSi11/Al2O3 joints

The subject of the work was to study the effect of Si alloying addition to the aluminum on the bond strength properties, wettability, and structure of interface in the AlSi11/Al₂O₃ joints. Taking advantage of the sessile drop method, the wetting of alumina substrates by liquid AlSi11 alloy or Al was studied. The sessile drop tests were carried out in the temperature range between 1023 and 1223 K, under a vacuum of 0.2 mPa for 30 or 120 minutes of contact. The shear strength results demonstrated significant improvement of shear strength of AlSi11/Al₂O₃ joints due to the application of silicon as an alloying addition to aluminum. Microstructural investigations of interface indicated that the silicon crystals were formed at the AlSi11/Al₂O₃ interface, which influenced the strengthening of these joints. A conclusion could be drawn, that the interface structure influenced the increase of the shear strength of AlSi11/Al₂O₃ joints.     

Design and Achievement of Metallurgical Bonding of Mg/Al Interface Prepared by Liquid–Liquid Compound Casting via a Co-deposited Cu–Ni Alloy Coating

The metallurgical bonding of Mg/Al bimetal by liquid–liquid compound casting was realized via co-deposition Cu–Ni alloy coating. The metallurgical layer of the Mg/Al bimetal consisted of Cu solid solution, Cu₂Mg and (Al0.7Cu1.3) Mg, Mg solid solution, Al₃Ni₂, and Mg₂Cu. Vickers hardness of the interface was between 149.9 and 209 HV, which was significantly lower than those of Al–Mg intermetallic compounds. The formation mechanism of the interface was attributed to interdiffusion among AZ91D, A356, and Cu–Ni alloy coating.

     

Mechanical and Wear Properties of Al–Al<Subscript>2</Subscript>O<Subscript>3</Subscript> Metal Matrix Composites Fabricated by the Combined Effect of Stir and Squeeze Casting Method

The effects of nano particles on double shear strength and tribological properties of A356 alloy reinforced with Al₂O₃ nano particles of size 30 nm were investigated. The percentage inclusions of Al₂O₃ were varied from 0.5 to 1.5 wt%. The particles were added with stirring at 400 rpm and squeeze casting at 750 °C and pressure of 600 MPa in a squeeze casting machine. Comparison of the performance of as cast samples of A356/Al₂O₃ nano composite was conducted. The tribological properties of the samples were also investigated by pin-on-disk tests at 10, 30 and 50 N load, sliding speed 0.534 m/s and sliding distance 1100 m in dry condition. SEM images of microstructure analysis of the composite, Al₂O₃ (0.5 and 1 %) particles were well dispersed in the A356 alloy matrix. Partial agglomeration was observed in metal matrix composite with higher (1.5 %) Al₂O₃ particle contents. The nano dispersed composites containing 0.5 and 1 wt% of Al₂O₃ nano particles exhibited the highest double shear strength, lesser wear loss and coefficient of friction.     

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.     

The Effectiveness of Surface Coatings on Preventing Interfacial Reaction During Ultrasonic Welding of Aluminum to Magnesium

High power ultrasonic spot welding (USW) is a solid-state joining process that is advantageous for welding difficult dissimilar material couples, like magnesium to aluminum. USW is also a useful technique for testing methods of controlling interfacial reaction in welding as the interface is not greatly displaced by the process. However, the high strain rate deformation in USW has been found to accelerate intermetallic compound (IMC) formation and a thick Al₁₂Mg₁₇ and Al₃Mg₂ reaction layer forms after relatively short welding times. In this work, we have investigated the potential of two approaches for reducing the IMC reaction rate in dissimilar Al-Mg ultrasonic welds, both involving coatings on the Mg sheet surface to (i) separate the join line from the weld interface, using a 100-μm-thick Al cold spray coating, and (ii) provide a diffusion barrier layer, using a thin manganese physical vapor deposition (PVD) coating. Both methods were found to reduce the level of reaction and increase the failure energy of the welds, but their effectiveness was limited due to issues with coating attachment and survivability during the welding cycle. The effect of the coatings on the joint’s interface microstructure, and the fracture behavior have been investigated in detail. Kinetic modeling has been used to show that the benefit of the cold spray coating can be attributed to the reaction rate reverting to that expected under static conditions. This reduces the IMC growth rate by over 50 pct because at the weld line, the high strain rate dynamic deformation in USW normally enhances diffusion through the IMC layer. In comparison, the thin PVD barrier coating was found to rapidly break up early in USW and become dispersed throughout the deformation layer reducing its effectiveness.     

Interaction Between Basal Slip and a Mg17Al12 Precipitate in Magnesium

We performed molecular dynamics simulations and investigated interactions between a Mg₁₇Al₁₂ precipitate and a basal dislocation in magnesium. Modified embedded-atom method potentials for multiple-component systems were used in our simulations. The simulation results show that the basal dislocation is able to shear through the matrix and the precipitate/matrix interface, without creating a loop around the precipitate. The precipitate is only elastically deformed by the external shear strain. This interaction can be considered an extreme case of the Orowan mechanism when the strength of the precipitate/matrix interface is weak. Cross slip of the basal dislocation was observed when the precipitate size was 3.0 nm. The dislocation changed its slip plane to another basal plane via the \( (01\overline{1} 0) \) prismatic and the \( (0\overline{1} 11) \) pyramidal planes, creating jogs on these non-basal planes. The jogs had low mobility and debris was created when the jogs were dragged forward by the Shockley partial dislocations.     

Thermochemical Analysis of Phases Formed at the Interface of a Mg alloy-Ni-plated Steel Joint during Laser Brazing

The thermodynamic stability of precipitated phases at the steel-Ni-Mg alloy interface during laser brazing of Ni-plated steel to AZ31B magnesium sheet using AZ92 magnesium alloy filler wire has been evaluated using FactSage thermochemical software. Assuming local chemical equilibrium at the interface, the chemical activity–temperature–composition relationships of intermetallic compounds that might form in the steel-Ni interlayer-AZ92 magnesium alloy system in the temperature range of 873 K to 1373 K (600 °C to 1100 °C) were estimated using the Equilib module of FactSage. The results provided better understanding of the phases that might form at the interface of the dissimilar metal joints during the laser brazing process. The addition of a Ni interlayer between the steel and the Mg brazing alloy was predicted to result in the formation of the AlNi, Mg₂Ni, and Al₃Ni₂ intermetallic compounds at the interface, depending on the local maximum temperature. This was confirmed experimentally by laser brazing of Ni electro-plated steel to AZ31B-H24 magnesium alloy using AZ92 magnesium alloy filler wire. As predicted, the formation of just AlNi and Mg₂Ni from a monotectic and eutectic reaction, respectively, was observed near the interface.     

Phase equilibria in Al-rich Al-Mg-Sc-Zn alloys at 430 and 300°C

Optical microscopy and X-ray diffraction and electron microprobe analyses are used to study Al-Mg-Sc-Zn alloys annealed at 430 and 300°C. The Al-based solid solution is found to be in equilibrium only with binary and ternary phases of the corresponding systems; these are Al₃Sc, β(Al₃Mg₂), η(MgZn₂), and τ(Al₂Mg₃Zn₃). Sections are constructed for the isothermal tetrahedra of the Al-Mg-Sc-Zn phase diagram that correspond to a scandium content of 0.5% and magnesium and zinc contents of up to 20%.     

Corrosion and mechanical properties of AM50 magnesium alloy after being modified by 1 wt.% rare earth element gadolinium

In order to improve the corrosion and mechanical properties of AM50 magnesium alloy, 1 wt.% Gd was used to modify the AM50 magnesium alloy. The microstructure, corrosion and mechanical properties were evaluated by X-ray diffraction(XRD), scanning electron microscopy(SEM), energy dispersive spectroscopy(EDS), electrochemical and mechanical stretch methods. The results indicated that β-Mg17Al12 phase decreased and Al2Gd3 and Al0.4GdMn1.6 phase existed after Gd addition. Because of the Gd addition, the grain of AM50 magnesium alloy was refined significantly, which improved the tensile strength of AM50 magnesium alloy. The decreasing of β phase improved the corrosion resistance of the magnesium alloy. The fracture mechanism of the Gd modified AM50 magnesium alloy was quasi-cleavage fracture. The corrosion residual strength(CRS) of AM50 magnesium alloy was improved after 1 wt.% Gd addition.     

Formation of Liquid and Intermetallics in Al-to-Mg Friction Stir Welding

In dissimilar-metal friction stir welding (FSW), intermetallic compounds can form in the stir zone and significantly reduce the joint strength. The formation of intermetallic compounds in Al-to-Mg FSW was investigated in lap and butt FSW of the widely used 6061 Al and AZ31B Mg and discussed using the binary Al-Mg phase diagram as an approximation. Temperature measurements during lap FSW indicated a 703 K (430 °C) peak temperature, slightly below the eutectic reaction (Mg) + Al₁₂Mg₁₇ → L at 710 K (437 °C), because the thermocouples were pushed downward during welding. The intermetallic compounds in the stir zone were revealed by color etching and identified by X-ray diffraction (XRD), electron probe microanalysis (EPMA), and transmission electron microscopy (TEM) as Al₃Mg₂ and Al₁₂Mg₁₇. Additional FSW was conducted near the edge of the upper sheet, and the liquid droplets squeezed out during welding solidified along the edge. Optical microscopy of the solidified droplets and EPMA revealed dendrites of Al₃Mg₂ and Al₁₂Mg₁₇ and interdendritic eutectics, thus indicating eutectic reactions (Mg) + Al₁₂Mg₁₇ → L (710 K (437 °C)) and (Al) + Al₃Mg₂ → L (723 K (450 °C)). Differential scanning calorimetry (DSC) confirmed that the solidified droplets melted at 709 K (436 °C) and 722 K (449 °C), nearly identical to the eutectic temperatures. Formation of intermetallic compounds on the order of 1 mm in size suggests they form upon solidification of the liquated material instead of solid-state diffusion.     

Cold Metal Transfer Welding of Dissimilar A6061 Aluminium Alloy-AZ31B Magnesium Alloy: Effect of Heat Input on Microstructure,Residual Stress and Corrosion Behavior

Lap joints of aluminum alloy A6061-T6 and AZ31B magnesium alloy were produced by cold metal transfer welding with Al-5 %Si filler metal. Four heat inputs designated as A (175 J/mm), B (185 J/mm), C (195 J/mm) and D (205 J/mm) were used during the process and the joints made were subjected to analysis of microstructure, mechanical properties and corrosion behaviour. The thickness of the fusion line (diffusion layer) varied from 3 to 12 µm depending on the heat input. It was also found that the joints made using the heat input of 205 J/mm exhibited highest tensile strength of 360 N/mm, least tensile stress in the weld and better pitting corrosion resistance. Electron microscopy study of the weld revealed the presence of β′-Mg₂Si, Al₆Mn and β-Al₃Mg₂ particles. X-ray diffraction study in the weld revealed the formation of γ-Al₁₂Mg₁₇ and β-Al₃Mg₂ phase with Mg₂Si strengthening precipitates. Tensile failure occurred at the fusion line near magnesium.     

Microanalytical study of the heterogeneous phases in commercial Al-Zn-Mg-Cu alloys

X-ray microanalysis and Convergent Beam Diffraction (CBD) studies were conducted on the second phase constituent and dispersoid particles in 7075 and 7475 aluminum alloys. Partial substitution of alloying elements was found to occur in all the second phase particles causing small deviations from the stoichiometric compositions reported for the binary and ternary compounds. The coarse constituent phases were identified to be Al₇Cu₂Fe, (Al,Cu)₆(Fe,Cu), Mg₂Si, α-Al₁₂Fe₃Si, amorphous silicon oxide, and a modified Al₆Fe compound in decreasing order of abundance. The dispersoid particles were Al₁₈Mg₃Cr₂ compound, and they formed in both triangular and spherical morphologies. Their compositions were found to vary slightly with the aging treatment. The crystal structure of the dispersoid phase consisted of a disordered form of a cubic structure (Fd3m) reported for the Al₁₈Mg₃Cr₂ compound. The uniqueness of CBD analysis in the crystal structure determination is emphasized.     

Strength Improvement Through Grain Refinement of Intermetallic Compound at Al/Fe Dissimilar Joint Interface by the Addition of Alloying Elements

Dissimilar material joining between Al alloys and steel may be effective in decreasing the weight of automobile bodies. In this study, dissimilar lap joining of Al alloys containing certain alloying elements, such as Ni, Cr, Mn, Ti, or Si, to interstitial-free steel was performed by tungsten inert gas arc brazing, and the effect of the alloying element on the joint strength associated with the Al-Fe intermetallic compound layer at the dissimilar interface was examined. The addition of an appropriate amount of an alloying element to the alloy increased the joint strength; the addition of Ni exhibited the most effective improvement. The additions of some elements changed the grain structure of the η-Fe₂Al₅ layer but not its chemical composition. This is the first study to clarify that smaller grain size of η-Fe₂Al₅ correlated to greater strength of the Al/Fe dissimilar joint.     

Effect of strontium on the microstructure, mechanical properties, and fracture behavior of AZ31 magnesium alloy

The effect of strontium (Sr) on the microstructure, mechanical properties, and fracture behavior of AZ31 magnesium alloy and its sensitivity to cooling rate are investigated. Three phases—blocky-shaped Mg₁₇Al₁₂, acicular Mg₂₀Al₂₀Mn₅Sr, and insular Mg₁₆(Al,Zn)₂Sr—are identified in the Sr-containing AZ31 alloys. With increasing cooling rate, the blocky-shaped Mg₁₇Al₁₂ phase increases, the acicular Mg₂₀Al₂₀Mn₅Sr phase diminishes, and the insular Mg₁₆(Al,Zn)₂Sr phase is refined and granulated. The study suggests that the grain size decreases with increasing cooling rate for a given composition. However, the grain size decreases first, then increases, and finally decreases again with increasing Sr for a given cooling rate. The yield strength (σ _y ) of AZ31 magnesium alloy can be improved by grain refinement and expressed as σ _y =35.88+279.13d ^−1/2 according to the Hall-Petch relationship. The elongation increases when Sr is added up to 0.01 pct and then decreases with increasing Sr addition. Grain refinement changes the fracture behavior from quasicleavage failure for the original AZ31 alloy to mixed features of quasicleavage and microvoid coalescence fracture.