In this study, the effect of arc mode in cold metal transfer (CMT) process on the porosity characteristic of additively manufactured Al-6.3%Cu alloy has been systematically investigated. The variants include conventional CMT, CMT pulse (CMT-P), CMT advanced (CMT-ADV) and CMT pulse advanced (CMT-PADV) and experiments were performed on both single layer deposits and multilayer deposits. The mechanism of porosity generation using the CMT arc mode variants is discussed. It was found that deposit porosity is significantly influenced by the arc mode type of CMT process. Conventional CMT is not suitable for the additive manufacturing process because it produces a large amount of gas pores, even in single layer deposit. CMT-PADV proved to be the most suitable process for depositing aluminium alloy due to its excellent performance in controlling porosity. With correct parameter, setting the gas pores can be eliminated. It was found that the key factors that enable the CMT-PADV process to control the porosity efficiently are the low heat input, a fine equiaxed grain structure and effective oxide cleaning of the wire.

Effect of arc mode in cold metal transfer process on porosity of additively manufactured Al-6.3%Cu alloy

Ti-6Al-4V alloy with two kinds of open cellular structures of stochastic foam and reticulated mesh was fabricated by additive manufacturing (AM) using electron beam melting (EBM), and microstructure and mechanical properties of these samples with high porosity in the range of 62%∼92% were investigated. Optical observations found that the cell struts and ligaments consist of primary α' martensite. These cellular structures have comparable compressive strength (4∼113 MPa) and elastic modulus (0.2∼6.3 GPa) to those of trabecular and cortical bone. The regular mesh structures exhibit higher specific strength than other reported metallic foams under the condition of identical specific stiffness. During the compression, these EBM samples have a brittle response and undergo catastrophic failure after forming crush band at their peak loading. These bands have identical angle of ∼45° with compression axis for the regular reticulated meshes and such failure phenomenon was explained by considering the cell structure. Relative strength and density follow a linear relation as described by the well-known Gibson-Ashby model but its exponential factor is ∼2.2, which is relative higher than the idea value of 1.5 derived from the model.

Compression deformation behavior of Ti-6Al-4V alloy with cellular structures fabricated by electron beam melting

Cold metal transfer (CMT) technology - An overview

Characterisation of the cold metal transfer (CMT) process and its application for low dilution cladding

Mechanical and microstructural properties of robotic Cold Metal Transfer (CMT) welded 5083-H111 and 6082-T651 aluminum alloys

The CMT short-circuiting metal transfer process and its use in thin aluminium sheets welding

Dissimilar weld joints in Ti3Al/TC4 were welded using the electron beam (EB) process. The microstructure evolution characterizations of the joints was investigated by means of OM, SEM, XRD, TEM and the tensile strengths of the joints were tested. The microstructure of the weld metal of every joint was identical. The structures were characterized by martensite, appearing coarse equiaxed grains. There existed grain coarsening and martensitic transformation in Ti3Al/HAZ and TC4/HAZ. With the increase of heat input, the grain size was significantly raised, yet the composition of the weld metal was independent of heat input. The highest tensile strength of the joints can reach 831 MPa, equaled almost to 92% of that of Ti3Al-based alloy.

Interfacial microstructure and strength of the dissimilar joint Ti3Al/TC4 welded by the electron beam process

A connecting method of an aluminum steel dissimilar metal pre-coating layer relates to the connecting method of the aluminum steel dissimilar metal. The connecting method solves the problems that the prior MIG melt-brazing method is limited by the wettability between an aluminum-based brazing filler metal and a steel plate, so the spreading performance of the brazing filler metal is poor on the steel plate, and the weld formation is poor. Acetone is used for wiping the surface of the steel plate and an aluminum plate, a brush is used for coating a paste which is stirred by the mixed powder and a binder on the surface of the steel plate, a lap joint is composed of the aluminum plate at the upper part and the steel plate at the lower part after the drying of the surface of the steel plate, a MIG welding machine is utilized for passing the melted aluminum plate, the steel plate is simultaneously maintained in a solid state, the self-fluxing brazing connection is formed at one side of the steel plate, and the melt welding connection is formed at the side of the aluminum plate to carrying out the welding of the lap joint. The connecting method improves the spreading performance of the aluminum-based brazing filler metal thereon and finally obtains the aluminum steel dissimilar metal joint with the beautiful shape, excellent mechanical performance and reliable strength, and the tensile strength of the joint can achieve more than 80 percent of an aluminum base material.

Aluminum steel dissimilar metal precoating connecting method

The droplet transfer and voltage-current characteristics of gas metal arc welding (GMAW) in single-pulsed GMAW (single GMAW-P), plasma pulsed GMAW (plasma GMAW-P), and plasma-GMAW-P with a magnetic field were studied using the synchronous acquisition system of high-speed camera and electric signals. The results showed the plasma arc and magnetic field had a significant effect on the droplet transfer process. The indirect arc of the plasma and gas metal arc emerged in the pulse peak phase causing a shunt phenomenon of the GMAW current. The period of the indirect arc was increased under the action of the magnetic field. In hybrid plasma GMAW-P, when the GMAW current did not exceed 140 A, several pulsed one-drop free transfers occurred and the droplet transfer period decreased with the increase in the plasma welding current; when the GMAW current exceeded 140 A, and the plasma welding current was less than 180 A, spray transfer was formed. The droplet transfer transformed into a projected transfer when the plasma welding current increased to 180 A. In plasma-GMAW-P hybrid welding with a magnetic field, the magnetic field had a slight effect on the transfer period. When the GMAW current did not exceed 140 A, the droplet transfer was mainly repelled transfer. The detaching location was on the right side of the wire when the magnetic field current was less than 3 A. When the magnetic field current exceeded 3 A, it was below or on the left side of the wire. When the GMAW current exceeded 140 A and the magnetic field current was less than 5 A, spray transfer was formed, but the droplet transfer mode transformed into a projected transfer with a magnetic field current of 5 A.

Jicai Feng

Papers

The CMT short-circuiting metal transfer process and its use in thin aluminium sheets welding

Interfacial microstructure and strength of the dissimilar joint Ti3Al/TC4 welded by the electron beam process

Aluminum steel dissimilar metal precoating connecting method

Characteristics of Magnetic Field Assisting Plasma GMAW-P