Al2Cu Precipitate Research Articles

Effect of intermediate processing treatment on the structure and mechanical properties of Al–4 wt%Cu–3 wt%Mn alloy manufactured by electromagnetic casting followed by high-pressure torsion (HPT)

In this work, a thermally stable model Al–4Cu–3Mn (wt%) alloy has been manufactured by electromagnetic casting (EMC), followed by compression, intermediate heat treatment and high-pressure torsion (HPT). Structural changes of the alloy during subsequent processing stages have been analysed by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and the X-ray diffraction (XRD). The results indicate that variations in the intermediate heat treatment temperature of the compressed samples lead to a significant difference in strain hardening and thermal stability after HPT. According to microstructure investigations the hardening of samples processed by HPT resulted from formation of mixture of grains and subgrains with high dislocation density as well as mechanical fragmentation of eutectic Al2Cu particles and precipitation of nanoscale Mn-rich dispersoids which are identified as Al6Mn. The intermediate heat treatment of the EMC rod at 350 ºC for 3 hours and heat treatment of HPT sample at 250 ºC for 5 hours exhibited the best mechanical properties in terms of ultimate tensile strength (UTS), yield strength (YS) and elongation (El), reaching 610 MPa, 560 MPa and 10 % respectively. At the same time intermediate annealing at 450 °C makes the HPT processing ineffective.

High strength and fatigue performance achieved for L-PBF processed hybrid particle reinforced Al-Cu-Mg composite

This study highlights the successful manufacturing of a crack-free, dense, hybrid ex-situ/in-situ particle reinforced (Ti + B4C)/Al-Cu-Mg composite, fabricated by laser powder bed fusion and exhibiting exceptional mechanical performance. In its as-built (AB) state, the composite displays a unique microstructure characterized by equiaxed grains with an average grain size of 1.0 ± 0.3 μm, notable interdendritic microsegregation of Cu, Mg, Mn, and Fe, randomly distributed ex-situ added Ti and B4C particles featuring a surface interaction layer with the metal matrix, and in-situ formed reinforcing particles, such as TiB2 and TiC. After subjecting the material to hot isostatic pressing (HIP) and subsequent aging treatment, dissolution of interdendritically segregated elements occurs, and precipitation of Al2Cu, Al12Mg17, and Al-Fe-Cu-Mn phases is observed. Significantly enhanced fatigue performance is recorded, reaching to 107 cycles at 250 MPa in AB and 330 MPa in HIP state, marking a 32 % improvement. The current study highlights the intricate relationship between the different microstructural features in AB and HIPed state, leading to fracture during tensile and fatigue loading conditions.

Unveiling the strengthening and toughening effects of copper-coated carbon nanotubes for the AlLiCu alloy matrix composite

Carbon nanotubes (CNTs) reinforced Al–Li–Cu alloy matrix composite is a promising candidate for the lightweight structural materials demanded in advanced industrial areas such as aerospace. However, how to fully exploit the combined strengthening effects of CNTs and precipitates of the Al–Li–Cu matrix is still an open issue. In the present study, the Cu coating was firstly precoated on CNTs before fabricating CNTs reinforced Al–Li–Cu alloy matrix composite. Benefiting from the Cu coating, the improved CNTs dispersion and Al-CNTs interfacial bonding was achieved, and the precipitation of Al2Cu, Al2CuLi, and Al3Li was enhanced in the AlLiCu alloy matrix, resulting in the enhanced strength-ductility synergy for Cu-coated CNTs reinforced AlLiCu alloy matrix composite. Moreover, strengthening and toughening mechanisms analyzation reveals that the Orowan strengthening of CNTs and precipitates, as well as load transfer strengthening of CNTs contribute mostly to the improved strength, while the increased ductility dominantly derives from the improved CNTs dispersion and Al-CNTs interfacial bonding, and the formation of low-density dislocation nanoregion (LDDN) in the interface area. This study not only opens up a new way for developing the AlLiCu alloy matrix composite reinforced by Cu-coated CNTs but also guides the microstructure regulation of other Al alloy matrix composites.

Effect of Mn/Ag Ratio on Microstructure and Mechanical Properties of Heat-Resistant Al-Cu Alloys.

This paper mainly investigated the effect of the Mn/Ag ratio on the microstructure and room temperature and high-temperature (350 °C) tensile mechanical properties of the as-cast and heat-treated Al-6Cu-xMn-yAg (x + y = 0.8, wt.%) alloys. The as-cast alloy has α-Al, Al2Cu, and a small amount of Al7Cu2 (Fe, Mn) and Al20Cu2 (Mn, Fe)3 phases. After T6 heat treatment, a massive dispersive and fine θ'-Al2Cu phase (100~400 nm) is precipitated from the matrix. The Mn/Ag ratio influences the quantity and size of the precipitates; when the Mn/Ag ratio is 1:1, the θ'-Al2Cu precipitation quantity reaches the highest and smallest. Compared with the as-cast alloy, the tensile strength of the heat-treated alloy at room temperature and high temperature is greatly improved. The strengthening effect of the alloy is mainly attributed to the nanoparticles precipitated from the matrix. The Mn/Ag ratio also affects the high-temperature tensile mechanical properties of the alloy. The high-temperature tensile strength of the alloy with a 1:1 Mn/Ag ratio is the highest, reaching 135.89 MPa, 42.95% higher than that of the as-cast alloy. The analysis shows that a synergistic effect between Mn and Ag elements can promote the precipitation and refinement of the θ'-Al2Cu phase, and there is an optimal ratio (1:1) that obtains the lowest interfacial energy for co-segregation of Mn and Ag at the θ'/Al interface that makes θ'-Al2Cu have the best resistance to coarsening.

Characterization of electromigration-induced short-range stress development in Al(0.25 at. % Cu) conductor line

Scanning x-ray microbeam topography and fluorescence experiments were conducted in situ to study the electromigration behavior of a 0.5 μm thick, 10 μm wide, and 200 μm long Al(0.25 at. % Cu) conductor line with 1.5 μm-thick SiO2 passivation on a single crystal Si substrate. The strain sensitivity of x-ray topography measurement allowed detailed examination of the electromigration-induced stress distribution and evolution in the conductor line in response to the depletion of Cu solute early in the electromigration process. Upon electromigration at 0.4 MA/cm2 and 303 °C, a short-range stress gradient was quickly induced by Al migration in the Cu-depleted cathode region to counteract further Al flow. The stress gradient was fully developed during the 5.3 h incubation time, extending over the critical Blech length of about 66 μm from the cathode end. Plastic deformation then occurred at the downstream end of the Cu-depleted region. The preferential electromigration of Cu did not cause detectable stress change outside the Cu-depleted region, except for the significant stress development from the Al2Cu precipitation at the anode end which appeared to initiate the fracture in the passivation. Preliminary finite difference modeling was undertaken to simulate the experimental observations, from which important parameters dictating electromigration in Al(Cu) line were extracted: an apparent effective valence of −5.6 and −1.9 for Cu and Al in Al(Cu), respectively, and a critical Cu concentration of 0.16 at. % above which Al grain boundary diffusion is effectively blocked.

Development of Graphitic 2024 Al Alloy by Mechanical Alloying

In this study, the 2024 Al powder with different weight fractions of graphite is mechanically milled using a high-energy ball mill for 3 hours each in the nitrogen environment. The milled powder is compacted at an elevated temperature. X-ray diffraction is used to phase analysis of milled powder as well as compacted specimens. Optical microscopy is used for microstructural analysis and hardness measurements are done for the evaluation of mechanical properties. The hot compacted specimens are also tested for their wear properties. Results show that there is no new phase formed during mechanical milling. But, after hot compaction of the milled powder, Al2Cu formed due to precipitation. No reaction is observed between the aluminum and the carbon (graphite) after milling as well as hot compaction. Microstructures of all hot compacted specimens are not showing pores, which, signifies full density after compaction. The formation of Al4C3 is not observed at any stage of processing. Therefore, graphite is uniformly distributed in all specimens, and the same is observed at grain boundaries of α-Al grains in the microstructures. Hardness increases with the addition of 1 wt.% graphite but it decreases with a further increase in graphite. The wear resistance of 2024 Al with 1 wt% graphite is the highest among all the compositions. The high hardness and wear resistance of 2024Al with 1 wt% graphite is the consequence of precipitation of Al2Cu during hot compaction and the presence of graphite which creates hindrances in the metal matrix. The presence of free graphite in the vicinity of grain boundaries acts as a solid lubricant which improves wear resistance of 2024 Al.

Effect of deformation parameters and Al2Cu evolution on dynamic recrystallization of 2219-O Al alloy during hot compression

The properties of Al alloy are significantly affected by the evolution of the microstructure during hot deformation. In this study, the 2219-O Al alloy was tested by hot compression at different temperatures, strain rates and compression ratios. Microstructures were analyzed at different parameters based on scanning electron microscopy and electron backscattered diffraction. With the temperature rising above 350 °C, more Al2Cu particles were dissolved. Instead, the increasing strain rate had a slightly positive effect on the precipitation of Al2Cu. The main dynamic recrystallization (DRX) mechanism in the 2219-O Al alloy was continuous dynamic recrystallization (CDRX) facilitated by fine Al2Cu particles. Particle stimulated nucleation (PSN) and discontinuous dynamic recrystallization (DDRX) were also observed. At 250–350 °C, the rising temperature gradually promoted the DRX with the stable content of fine Al2Cu particles. At 350–450 °C, the decrease of Al2Cu particles with rising temperature weakened the DRX. At 490 °C, all fine Al2Cu particles were dissolved, and the extremely high temperature significantly promoted the migration of grain boundaries, strengthening the DRX. The decreasing strain rate and increasing strain facilitated the DRX.

Fatigue response of a cast Al-Cu-Mg-Ag-TiB2 (A205) alloy: Stress relieved and aged

The purpose of this study is to assess the influence of heat treatment on the fatigue behavior of cast A205 alloy (i.e., Al-Cu-Mg-Ag-TiB2 nanocomposite). To do so, A205 samples were heat-treated and divided into two categories (i) stress-relieved (SR) and (ii) T7 stabilizing over-aged. This research delves further into the microstructure, mechanical properties, and fatigue performance of A205 alloy in SR and T7 heat-treated (i.e., T7 aged) conditions. After production and post-heat treatments, the samples underwent force-controlled fatigue experiments, tensile and depth-sensing indentation testing, and advanced microstructural characterizations (using electron backscattered diffraction and transmission electron microscopy). Microstructural characterization revealed exceptionally equiaxed, texture-free microstructure with uniform grain distribution and the existence of Al2Cu precipitates and TiB2 particles. The T7 heat treatment did not change grain size significantly (grain size: 46.4 ± 13.5 µm for SR and 48.5 ± 13.7 µm for T7 material). The T7 heat treatment was found to be very effective in improving the fatigue resistance of A205. The higher fatigue resistance of cast T7 material is attributed to the accelerated precipitation of Al2Cu along with different habit planes. The results of this study offer a critical understanding for choosing the optimum heat treatment parameters to control the fatigue behavior of cast A205, which is crucial considering their applications in the aerospace industry.

Improved Thermo-Mechanical Fatigue Resistance of Al-Si-Cu 319 Alloys by Microalloying with Mo.

Thermo-mechanical fatigue (TMF) is one of the most detrimental failures of critical engine components and greatly limits their service life. In this study, the out-of-phase TMF (OP-TMF) behavior in Al-Si-Cu 319 cast alloys microalloyed with Mo was systematically investigated under various strain amplitudes ranging from 0.1-0.6% and temperature cycling at 60-300 °C and compared with the base 319 alloy free of Mo. Cyclic stress softening occurred in both experimental alloys when applying the TMF loading, resulting from the coarsening of θ'-Al2Cu precipitates. However, the softening rate of the Mo-containing alloy was lower than that of the base 319 alloy because of its lower θ'-Al2Cu precipitate coarsening rate per cycle. The Mo-containing alloy exhibited a longer TMF lifetime than the base alloy at the same strain amplitude. Microalloying 319 alloy with Mo enhanced the TMF resistance mainly by slowing the coarsening of θ'-Al2Cu precipitates and providing supplementary strengthening from thermally stable Mo-containing α-dispersoids distributed in the Al matrix. The energy-based model was successfully applied for predicting the TMF lifetime with a low life predictor factor, which agreed well with the experimentally measured fatigue cycles.

Effects of thermal ageing on the wear behavior of the cerium modified Al-18si-3.6cu alloy

ABSTRACT In the present investigation, an Al-18Si-3.6Cu alloy was modified by cerium (Ce), heat treated (T6), and aged for 1, 3, 5, and 7 h at 210°C. The resulting microstructures revealed that the addition of Ce as a modifier changed the morphology of the primary Si from coarse with a sharp edge to spherical, large-acicular/needle-like eutectic Si into a fibrous state, and dendrites of the Al phase into round branches with less interface separation. After thermal ageing, the microstructure of the modified alloy revealed no change in the morphology of the primary Si phase. However, a considerable change in the eutectic Si phase and the formation of fine precipitates of Al2Cu and Al2CeSi intermetallics in the matrix. Hardness was found to be significantly higher in the modified and age-hardened alloys. A Pin-on-disc wear tester was used to investigate the dry sliding wear behavior of alloys at different loads (10, 20, 30, and 40 N) and 1.0 m/s sliding velocity. The results indicated that the wear rate in the modified alloy was lower than the base alloy. Furthermore, the modified alloy after 5 h age hardening demonstrated high wear resistance and improved wear bearing capacity compared to the 1, 3, and 7 h age hardened alloys.

Understanding the effect of low melting-point phases and homogenization annealing on the liquation cracks formation in the Al-Cu binary system during laser melting process

The alloy design is vital mission for eliminating the laser melting and additive manufacturing technologies defects. The low melting-point phases around the grain boundaries are considered as a source of the liquation cracks formation during laser melting process (LMP). In this work, a simple Al-Cu binary alloy with different Cu concentrations was selected as a model to understand the relation between low-melting point phases and liquation cracks formation during the LMP. In cast samples, most Al2Cu (θ phases) precipitate at the α-Al grain boundaries and during the LMP, the liquation cracks in the laser-melted zone (LMZ) initiated at the grain boundaries and propagated along the LMZ. Thus, homogenization annealing pre-laser melting at various times was done. The results showed that the cast Al-3.5Cu revealed high cracks susceptibility in the LMZ due to the presence of high amount of θ phases and during homogenization annealing the phases dissolved and the number of cracks significantly decreased. No cracks were formed in Al-7.5Cu at the cast and homogenized conditions due to the presence of many equilibrium eutectic θ phases, which heals the cracks (backfilling) during the solidification after the LMP. Liquation cracks susceptibility can be controlled by homogenization annealing.

Effect of thermo-mechanical distribution on the evolution of IMCs layer and mechanical properties of 2219 aluminum alloy/304 stainless steel joints by inertia friction welding

The hybrid structure of 2219 aluminum alloy (Al alloy) and 304 stainless steel is effectively joined by inertia friction welding. There are the Cu-rich layer and the Fe4Al13 layer in the friction interface. The Cu-rich layer is discontinuous and its thickness is not uneven. While the Fe–Al layer is continuous and its thickness is closely related to the thermo-mechanical distribution at the interface. The thickness of the Fe–Al IMCs layer in the 1/2 radius zone is 6 fold of that in the center, while the center zone has unbonding defects due to low temperature and poor plastic flow of Al alloy. However, after changing the shape of the Al alloy end face, especially for the tapering surface joint, the homogeneous layer of Fe–Al IMCs forms in the center and 1/2 radius zones, which makes the tensile strength of different zones of the joint more balanced and improves the integral tensile strength. Meanwhile, the evolution of the two IMCs layers was investigated. It is found that the Cu-rich layer is formed through the precipitation of Al2Cu in the Al alloy. While the Fe–Al layer is formed through atomic interdiffusion and its growth is influenced not only by the thermo-mechanical coupling but also the precipitation of the Al2Cu phase.

Improvement of the Mechanical Properties of the Diffusion-Bonded 2024 Aluminum Alloy through Post-Weld Heat Treatments

In this study, 2024 aluminum alloy was diffusion bonded to identify the effect of the bonding temperature, applied pressure, and heating time on the microstructure, hardness, and bonding strength. The shear strength increased from 62.5 MPa to 81.2 MPa along with the rise in bonding temperatures from 440 °C to 490 °C. The bonding strength rose from 62.5 MPa to an optimal value of 81.2 MPa by extending the bonding time from 30 min to 240 min at a bonding temperature of 490 °C and a constant pressure of 5 MPa. In addition, various post-weld heat treatments for diffusion-bonded joints were also performed to improve the bond quality. After the T6 or T4 post-weld heat treatment, the hardness at the bonding interface and the substrate increased due to the precipitation of Al2Cu. Post-weld T4 and T6 heat treatments increased the interface microhardness from 106.3 Hv to 138.25 Hv and 130.6 Hv, respectively. The bonding strength of the AA2024 was significantly improved up to 124.5 MPa and 164.3 MPa by the T4 and T6 heat treatments, respectively.

Influence of boride, oxide, and carbide ceramics as secondary reinforcement in T6-A333 functionally graded hybrid composites

Hybrid ceramics in functionally graded aluminium hybrid composites are a developing choice for the maritime industries to maximize their daily mechanical and tribological demands. Ceramic types, including borides, oxides, and carbides, have a key impact in regulating the tribo-mechanical performance of hybrid composites. The external addition of Mg potentially lowered the wetting angle along with the matrix-ceramic interface. This study compares the mechanical and tribological performance of 6 wt%B4C/4 wt%TiB2/A333, 6 wt%B4C/4 wt%ZrO2/A333, and 6 wt%B4C/4 wt%TiC/A333 hybrid composites. Hybrid reinforcement in functionally graded composites enable the designers in modern manufacturing to eliminate the challenges like porosity and insufficient wettability. Advance characterizations highlight the morphological phase transformations undergone with heat treatment, contributing towards increase in composite performance. Coarse patches of Mg2Si and air-foil shaped Al2Cu precipitate operate as a strengthening agent that withstands shear. TiC-rich outer wall zone of hybrid composite demonstrated maximum microhardness (202.7 HV) and tensile strength (256.2 MPa). Zonal dominance of ceramic variants as secondary reinforcement minimizes wear and third body abrasion. Wear debris analysis indicates creating a mechanically mixed layer, which affects the friction along with the sliding interface. Passivation and interfacial pitting are the main corrosion mechanisms found in a saline environment when TiC particles act as a secondary ceramic.

Effects of milling time on sintering properties and formation of interface Al4C3 on graphite reinforced Al-4.5Cu-1.5Mg nanocomposite

Aluminum-based metal matrix nanocomposites have been extensively researched and developed for aerospace and automotive applications. Al-4.5Cu-1.5Mg with 0.5 wt% graphite were milled for 2 h, 4 h, 6 h, and 8 h using shaker mill under argon gas. The phenomena of deformation, fracturing, and cold welding during shaker mill were investigated to observe how the shaker mill effects on their morphology and formation of intermetallic phases due to its very high speed. Sintering under ultra-high purity argon gas for 99.9999% was done to produce high density materials. Intermetallic phase Al4C3 was found as a result reaction between aluminum and graphite during milling. Formation of Al4C3 is very important to the alloy as an interface between matrix and reinforcement particle in order to have higher hardness. A decrease in Peaks Cu and followed by an increase in Al2Cu precipitation in the XRD pattern occurred with increasing milling time. The role of Al2Cu precipitation is very important in improving mechanical properties, resulting in the highest hardness value reaching 97 HV and a density value of 83% at 8 h of milling.

The improved strength and ductility of ZrCp/2024Al composites with a quasi-network microstructure fabricated by spark plasma sintering and T6 heat treatment

In this study, the 2024Al alloy improved by the various fraction of ZrC particles (ZrCp/2024Al composites) were constructed and processed through the spark plasma sintering (SPS) combined with T6 heat treatment in order to improve the strength and toughness simultaneously. The microstructure observations revealed that the interfacial bond between the ZrC and aluminum matrix was satisfactory and the quasi-network distribution of ZrC particles was demonstrated. The precipitates of Al2Cu and Al2CuMg, dissolved out from the 2024Al and ZrCp/2024Al composite during ageing process, exhibited little different in size and shape. With the introduction of ZrC particles, the ageing behavior was expedited and the time to achieve the aged hardness was prominently shortened from 12 h to 6 h as 5.0 wt% ZrC particles were introduced. The accelerated aging process benefited from dislocations, caused by the mismatch of thermal expansion coefficients between the ZrC and matrix. The ultimate hardness, yield strength, tensile strength and strain were all enhanced with the addition of ZrC particles. When 4.0 wt% ZrC particles were applied to the composites, the highest yield strength, tensile strength with superior ductility (332 MPa, 495 MPa and 12.0%) was obtained, which were 48.2%, 34.5% and 23.7% higher than that of pure 2024Al respectively. The improved tensile strength and strain are contributed to the particularly inhomogeneous quasi-network structure, which made the matrix deformation blocked, dislocation motion impeded and crack propagation path increased.

Influence of CeO2 reinforcement on microstructure, mechanical and wear behaviour of AA2219 squeeze cast composites

The present investigation deals with development of AA2219 composites with different weight fractions of Cerium oxide (CeO2) reinforcement and characterizing the microstructure and mechanical properties thereof. XRD and SEM micrograph confirm the presence of CeO2 particles and Al2Cu precipitate. The grain size of 0, 0.5, 1.0, 1.5 and 2 wt% CeO2 composites are 483, 453, 411, 362 and 328 μm, respectively. Addition of CeO2 significantly reduces the dendritic morphology and refines the α-Al grain structure. 2 wt% CeO2 addition has yielded the maximum hardness of 124 HV and yield strength of 87 MPa in all the composites developed. Additionally, the developed composites were evaluated by examining the wear characteristics with the co-efficient of friction (COF) and the specific wear rate. In this study, Taguchi's L25 orthogonal array was used to optimize the parameters like reinforcement fraction, load and sliding distance. Signal-to-noise ratio (S/N ratio) and analysis of variance (ANOVA) are used to obtain the parameters highly influencing the wear behaviour. Adhesive wear is exhibited by ploughing at lower loads and delamination is observed with increasing load. Deep shallow ploughs with embarked abrasion are observed at higher loads.

Fabrication and characteristic of 2024Al matrix composites reinforced by carbon fibers and ZrCp by spark plasma sintering

The 2024Al matrix composite reinforced with bimodal-scaled reinforcement phases, carbon fibers and ZrC particles, was designed and prepared by spark plasma sintering for the purpose of obtaining high strength and good ductility. The microstructural observation shows that the ZrC particles mixed with the Al2Cu and Al2CuMg precipitate phases formed a quasi-network architecture. The Ni coating electroless plated on the carbon fiber can improve the interfacial bonding strength by the chemical reactions of Ni-P coating and matrix as well as prevent the reaction of carbon fiber and 2024Al. As expected, the tensile strength and ductility of bimodal-size reinforced composites with peculiar quasi-network structure showed a significant improvement in comparison with the 2024Al matrix alloy and monolithic carbon fibers or ZrC particles reinforced composites. The 2024Al matrix composites strengthened with carbon fibers and ZrC particles exhibit the tensile strength and elongation of 330 MPa and 10.2%, which are 39.2% and 229% higher than the 2024Al matrix. The excellent enhancement effect is owing to load transfer effect, quasi-network structure strengthening, precipitation refinement, Orowan strengthening as well as dislocation strengthening.

Quantifying the effects of Sn on θ′-Al2Cu precipitation kinetics in Al–Cu alloys

In this study, the effects of 0.14 wt-% Sn on accelerating the precipitation kinetics during heat treatment are quantified. By calculating the activation energy of θ′ phase, it was found that the combined additions of Cu and Sn can reduce the energy barrier and increase the number density of the θ′ phase in the peak aged state, and thus improving yield strength and ultimate tensile strength from 239 and 318 to 445 and 457 MPa, respectively. Based on the quantitative analysis of the θ′ phase, it was found that with the combined additions of Cu and Sn, the average length of the θ′ phase increased from 18.11 to 25.82 nm, and the number density increased from 2.17 × 1021 to 4.62 × 1021 m−3.

Interfacial microstructural characterization and mechanical properties of inertia friction welding of 2219 aluminum alloy to 304 stainless steel

Aluminum alloy/steel hybrid components are receiving more and more attention in recent years due to their great potential in reducing weight while maintaining the mechanical properties of the structure. Inertia friction welding was performed to join 2219 aluminum alloy (Al alloy) bar to 304 stainless steel bar. The effects of welding parameters on the evolution of intermetallic compounds (IMCs) and tensile strength of the joints were investigated. High-quality welded joints can be obtained at the parameters combination of the medium friction pressure (120 MPa) and low rotational speed (1100 rpm) from the experimental study. Microstructural analyses indicated that the enrichment of Cu element at the friction interface formed Al2Cu IMCs instead of Fe-Al IMCs, which was usually reported to exist at the Al alloy/steel friction welded interface. The formation of the Al2Cu IMCs layer was mainly attributed to the accumulation of Al2Cu (precipitate in 2219 Al alloy base metal) at the wavy surface of the steel, significantly promoting the growth of Al2Cu by the subsequent precipitation process. However, cracks could easily occur in a thicker Al2Cu IMCs layer at a high heat input, which seriously deteriorated the mechanical properties of joints. Therefore, the massive formation of the Al2Cu IMCs layer should be suppressed by controlling the welding parameters to avoid any internal cracks at the weld interface.