Effect of Ni Coating on Microstructure and Property of Al Alloy/Steel CMT Welding-Brazing Joints

Abstract

The cold metal transfer (CMT) welding-brazing process was chosen to join Al alloy and Ni-coated steel using AlSi12 as the filler wire. The macrostructure and microstructure of the joints were tested by using an optical microscope (OM), scanning electron microscope (SEM), energy dispersive spectrometry (EDS), and X-ray diffraction (XRD). The tensile properties and corrosion properties of the joints were also tested. The results showed that Ni coating could improve the wettability and spreadability of molten AlSi12 filler metal on the steel surface, resulting in a good appearance for the Al alloy/steel joint. Ni coating could hinder the chemical metallurgical reaction between Al atom and Fe atoms to inhibit the formation of brittle Fe-Al intermetallic compounds (IMCs) and reduce the thickness of the IMCs layer. Meanwhile, the Ni atom reacted with the Fe and Al atoms to form Al3Ni2, (Fe, Ni) Al3 and (Fe, Ni)2Al3, which improved the tensile strength of the joints. All joints with Ni coating cracked near the Al alloy. When the Ni-coating thickness was 5 μm, the tensile strength of the joint reached a maximum of 202.5 MPa. The addition of Ni could also improve the corrosion resistance of the joints. Significantly, when the Ni-coating thickness was 10 μm, most of the Ni coating was still solid, and the interface reaction layer was mainly composed of α-Ni solid solution and some (Fe, Ni)2Al3.

Corrosion fatigue mechanisms and evaluation methods of high‐strength steel wires: A state‐of‐the‐art review

“…Macroscopic corrosion feature analysis. 54 [Colour figure can be viewed at wileyonlinelibrary.com] types follows a generalized extreme value distribution.…”

1000 °C High-Temperature Wetting Behaviors of Molten Metals on Laser-Microstructured Metal Surfaces

“…However, only few literature studies focused on the wettability of molten metals at high temperatures (e.g., 1000 °C) compared with the wettability studies on more common liquids under more gentle conditions, such as water and low-melting-point liquid metals at room temperature. − Various simulations have been performed to predict the probable wetting behaviors of molten metals on various substrates, − but practical observations remain scarce due to the availability of materials and the strict environmental requirements. Among the restricted experimental work, researchers prefer to improve the wettability of molten metals with several kinds of solid surfaces for better performance in welding, brazing, metal-based composite formation, and lithium battery preparation. − ,− For example, Wu et al proposed a method to enhance the wettability of a kind of room-temperature gallium-based liquid metal on polyacrylate surfaces for a better connection, Fan et al modified the wetting and spreading behaviors of Sn on the SiC surface by changing the content of the alloying element Cr, Li et al enhanced the wettability of molten high manganese steel with Ni–Co-coated ZTA ceramic particles to strengthen the abrasive wear resistance of the composites, and Sui et al studied the wetting ability of molten Ce and Cu–Ce alloy on various carbon materials. Liu et al introduced ultrasonic power to improve the wetting of the Zn filler on the TC4 alloy and further strengthen the mechanical properties of the brazed joint, and Griffith et al investigated the effect of droplet size on the wetting behaviors of molten Sn on copper substrates for better performance of microsolder joints.…”

“…On the other hand, limited publications studied the effect of surface microstructures on the wetting behaviors of molten metals on substrates at high temperatures, while most of them concerned about the composition of the melts and the substrate surfaces or the periphery conditions. − ,,− , Lai et al found that a microporous copper substrate enhanced the wetting of molten Sn, while Zhou et al structured the steel mold surfaces to weaken the adhesion of the molten and resolidified Al alloys with the mold by preventing their full wetting. Liu et al discussed the effect of laser-textured stainless steel surface structures on the wetting and spreading behaviors of the Al–Si alloy in the presence of flux, and Lin et al observed that rough silica surfaces improved the spreading of the Sn–Ag–Ti alloy.…”

Research on the Microstructure and Properties of Al Alloy/Steel CMT Welding-Brazing Joints with Al–Si Flux-Cored Welding Wires

“…With the acceleration of China's "carbon neutrality" process, the trend of "replacing steel with Al alloy" in the industrial field is becoming more and more obvious [1,2]. Especially with the explosive growing demand for Al alloy to be used in the field of new energy vehicles and solar photovoltaics, composite structures of lightweight Al alloy and high-strength steel have been widely used [3,4]. However, the weldability of an Al alloy and low carbon steel, or stainless steel, is poor due to the differences in crystal structure and the physical and chemical properties between them [5][6][7].…”