The strengthening effect of inter-layer cold working and post-deposition heat treatment on the additively manufactured Al-6.3Cu alloy

Wire + Arc Additive Manufacture (WAAM) attracts great interest from the aerospace industry for producing components with aluminum alloys, particularly Al-Cu alloy of the 2000 series such as 2219 alloy. However the application is restricted by the low strength properties of the as-deposited WAAM metal. In this study two strengthening methods were investigated - inter-layer cold working and post-deposition heat treatment. Straight wall samples were prepared with 2319 aluminum alloy wire. Inter-layer rolling with loads of 15 kN, 30 kN and 45 kN were employed during deposition. The ultimate tensile strength (UTS) and yield strength (YS) of the inter-layer rolled alloy with 45 kN load can achieve 314. MPa and 244. MPa respectively. The influence of post-deposition T6 heat treatment was investigated on the WAAM alloy with or without rolling. Compared with inter-layer rolling, post-deposition heat treatment can provide much greater enhancement of the strength. After T6 treatment, the UTS and YS of both of the as-deposited and 45 kN rolled alloys exceeded 450. MPa and 305. MPa respectively, which are higher than the properties of the wrought 2219-T6 alloy. The strengthening mechanisms of this additively manufactured Al-6.3Cu alloy were investigated through microstructure analysis

Residual stress of as-deposited and rolled Wire + Arc Additive Manufacturing Ti–6Al–4V components

Wire + arc additive manufacturing components contain significant residual stresses, which manifest in distortion. High-pressure rolling was applied to each layer of a linear Ti–6Al–4V wire + arc additive manufacturing component in between deposition passes. In rolled specimens, out-of-plane distortion was more than halved; a change in the deposits' geometry due to plastic deformation was observed and process repeatability was increased. The Contour method of residual stresses measurements showed that although the specimens still exhibited tensile stresses (up to 500 MPa), their magnitude was reduced by 60%, particularly at the interface between deposit and substrate. The results were validated with neutron diffraction measurements, which were in good agreement away from the baseplate

Microstructure and mechanical properties of double-wire + arc additively manufactured Al-Cu-Mg alloys

As the properties of wire + arc additively manufactured Al-6.3Cu alloy cannot meet the applying requirements, a double-wire + arc additive manufacturing system was built to add magnesium into Al-Cu deposits for higher mechanical properties. Two commercial binary wires aluminum-copper ER2319 and aluminum-magnesium ER5087 were chosen as the filler metal to build Al-Cu-Mg components with different compositions by adjusting the wire feed speed. The microstructure and morphology of thin wall samples were characterized by optical micrographs (OM), X-ray diffraction (XRD) and scanning electron microscopy (SEM). The Vickers hardness and tensile properties were investigated. The microstructure of Al-Cu-Mg deposits was mainly composed of coarse columnar grains and fine equiaxed grains with non-uniformly distributing characteristics. With higher Cu but lower Mg content, the strengthen phase turned to Al2Cu + Al2CuMg from Al2CuMg, and the micro hardness presented an increasing trend. The isotropic characteristics of ultimate tensile strength (UTS), yield strength (YS) and elongation were revealed in these samples. The UTS was about 280 ± 5 MPa both in horizontal and vertical directions for all samples. The YS showed an increasing trend from 156 MPa to 187 MPa with the same content trend, while elongation decreased from 8.2% to 6%. The fractographs exhibited typical brittle fracture characteristics

A comparative study of additively manufactured thin wall and block structure with Al-6.3% Cu alloy using cold metal transfer process

In order to build a better understanding of the relationship between depositing mode and porosity, microstructure, and properties in wire + arc additive manufacturing (WAAM) 2319-Al components, several Al-6.3%Cu deposits were produced by WAAM technique with cold metal transfer (CMT) variants, pulsed CMT (CMT-P) and advanced CMT (CMT-ADV). Thin walls and blocks were selected as the depositing paths to make WAAM samples. Porosity, microstructure and micro hardness of these WAAM samples were investigated. Compared with CMT-P and thin wall mode, CMT-ADV and block process can effectively reduce the pores in WAAM aluminum alloy. The microstructure varied with different depositing paths and CMT variants. The micro hardness value of thin wall samples was around 75 HV from the bottom to the middle, and gradually decreased toward the top. Meanwhile, the micro hardness value ranged around 72–77 HV, and varied periodically in block samples. The variation in micro hardness is consistent with standard microstructure characteristics

Assessing the effect of TIG alternating current time cycle on aluminium wire + arc additive manufacture

The effect of electrode positive time cycle (% EP) of the alternating current TIG process has been investigated for aluminium wire + arc additive manufacture of linear walls. The study considered the effect on oxide removal, linear wall dimensions, microstructure, mechanical properties as well as the effect on electrode wear. The results showed that the effective wall width was minimum at 20%EP with a corresponding maximum in layer height. It was also observed that increasing the% EP increased the electrode wear rate, which in turn affected the arc stability. Microstructure analysis showed a noticeable increase in the grain size for higher% EP. The study also showed that% EP had no significant effect on mechanical properties. From a heat input analysis, a direct correlation was observed between the arc voltage and the% EP. The study also indicated that there could be other contributing factors to wall dimensions. For aluminium wire + arc additive manufacture of linear walls, minimum cleaning ranged between 10%EP and 20%EP

Properties of wire+ arc additively manufactured 2024 aluminum alloy with different solution treatment temperature

2024 aluminum alloy deposits were produced with wire + arc additive manufacturing procedure. Solution treatment + natural aging processes with different solution treatment temperature were conducted to improve the properties. The microstructure and mechanical properties were investigated. After heat treatment the distributing characteristic of the second phase changed to be dispersive from continuous in as-deposited condition. Solution treatment + natural aging process can significantly improve the properties of WAAM 2024 aluminum alloy. With higher solution treatment temperature, the micro hardness, tensile properties and elongation presented an increasing trend. After 503 °C solution treatment + natural aging process, the micro hardness, ultimate tensile strength, yield strength and elongation were 143HV, 497 MPa, 330 MPa and 16%, respectively, which can nearly meet the applying requirement

Numerical investigation of the effect of rolling on the localized stress and strain induction for wire + arc additive manufactured structures

Cold rolling can be used in-process or post-process to improve microstructure, mechanical properties and residual stress in directed-energy-deposition techniques, such as the high deposition rate wire + arc additive manufacturing (WAAM) process. Finite element simulations of the rolling process are employed to investigate the effect of rolling parameters, in particular rolling load and roller profile radius on the residual stress field as well as plastic strain distribution for the profiled roller. The results show the response to rolling of commonly used structural metals in WAAM, i.e., AA2319, S335JR steel and Ti-6Al-4V, taking into account the presence of residual stresses. The rolling load leads to changes in the location and the maximum value of the compressive residual stresses, as well as the depth of the compressive residual stresses. However, the roller profile radius only changes the maximum value of these compressive residual stresses. Changing the rolling load influences the equivalent plastic strain close to the top surface of the wall as well as in deeper areas, whereas the influence of the roller profile radius is negligible. The plastic strain distribution is virtually unaffected by the initial residual stresses prior to rolling. Finally, design curves were generated from the simulations for different materials, suggesting ideal rolling load and roller profile combinations for microstructural improvement requiring certain plastic strains at a specific depth of the additive structure

Control of residual stress and distortion in aluminium wire + arc additive manufacture with rolling

The aluminium alloy wire 2319 is commonly used for Wire + Arc Additive Manufacturing (WAAM). It is oversaturated with copper, like other alloys of the precipitation hardening 2### series, which are used for structural applications in aviation. Residual stress and distortion are one of the biggest challanges in metal additive manufacturing, however this topic is not widely investigated for aluminium alloys. Neutron diffraction measurements showed that the as-built component can contain constant tensile residual stresses along the height of the wall, which can reach the materials' yield strength. These stresses cause bending distortion after unclamping the part from the build platform. Two different rolling techniques were used to control residual stress and distortion. Vertical rolling was applied inter-pass on top of the wall to deform each layer after its deposition. This technique virtually elimiated the distortion, but produced a characteristic residual stress profile. Side rolling instead was applied on the side surface of the wall, after it has been completed. This technique was even more effective and even inverted the distortion. An interesting observation from the neutron diffraction measurements of the stress-free reference was the significantly larger FCC aluminium unit cell dimension in the inter-pass rolled walls as compared to the as-build condition. This is a result of less copper in solid solution with aluminium, indicating greater precipitation and thus, potentially contibuting to improve the strenght of the material

Micropore evolution in additively manufactured aluminum alloys under heat treatment and inter-layer rolling

The application of wire + arc additively manufactured (WAAM) aluminum alloys has been restricted by the porosity defect, which is generally detrimental to the mechanical properties. Suppressing of micropores in the WAAM components has attracted considerable attention in recent years. Inter-layer rolling was introduced to eliminate micropores during the WAAM deposition of the Al–Cu6.3 and Al–Mg4.5 alloys. The distribution characteristics and individual morphology of micropores were revealed by the X-ray diffraction tomography. Key findings demonstrated that the number, volume, size, and roundness of micropores in rolled alloys decreased similarly with increasing loads, eventually achieving a density of over 99.9%. After the heat treatment, the homogeneous distribution of fine (around 5.3 μm) and spherical (0.70–0.74) micropores was realized in the 45 kN rolled alloys. All the evaluated indicators of micropores in the 45 kN rolled + heat treated alloys were superior to the post-deposition heat treated state. The evolution mechanisms include the reprecipitation of hydrogen pores, formation of vacant voids, and re-opening of unclosed pores. The hybrid technique of WAAM + rolling + heat treatment has great potential in promoting mechanical properties of WAAM alloys. The results will provide a theoretical guidance for the design of high-performance WAAM aluminum alloy components