Short communication
Ultralow rotation speed produces high-quality joint in dissimilar friction welding of Ti–6Al–4V alloy and SUS316L stainless steel

https://doi.org/10.1016/j.msea.2020.140303Get rights and content

Highlights

  • Ultralow rotation speed and high friction pressure were innovatively adopted.

  • Ultralow rotation speed suppressed the mechanically mixed layers and cracks.

  • High friction pressure produced a thin and strong intermetallic compound layer.

  • High friction pressure provided a large faying-surface deformation for SUS316L.

  • A high-quality Ti–6Al–4V/SUS316L friction weld joint was simply fabricated.

Abstract

Ultralow rotation speed and high friction pressure were adopted to friction weld Ti–6Al–4V alloy and SUS316L stainless steel. Ultralow rotation speed effectively suppressed the formation of harmful mechanically mixed layers. High friction pressure guaranteed a proper welding temperature and a sufficient SUS316L deformation. A high-quality joint was then successfully fabricated.

Introduction

The dissimilar welding of titanium alloys and stainless steels has attracted much attention in abundant industrial fields such as chemical, cryogenic, nuclear, and biomedical since it is capable to incorporate their respective advantages to provide lightweight, low-cost, great corrosion resistance and excellent biocompatibility simultaneously [[1], [2], [3], [4], [5]]. Conventional fusion welding has been adopted to weld titanium alloys and stainless steels [[3], [4], [5], [6], [7], [8]], however, it seems difficult because their greatly different physical/chemical properties are prone to induce severe welding distortion and large residual stress, and the thick intermetallic compound (IMC) layers caused by a high temperature are susceptible to fracture making the joints brittle. Solid-state joining techniques are therefore required to weld titanium alloys and stainless steels. Friction welding (FW) is one of the solid-state joining techniques, where the friction heat is generated at the weld interface to soften the interface materials, then they are plasticized out to the outer region to form the joint. As the FW avoids the fusion-welding-related issues and allows a faster welding process than diffusion welding, it has been increasingly adopted to weld titanium alloys and stainless steels [[9], [10], [11], [12], [13], [14], [15]]. For most of the correlated studies, researchers always implemented the welding processes under low friction pressures and high rotation speeds. P. Li et al. [10] performed the FW of Ti–6Al–4V (Ti64) alloy and 316L stainless steel using a low friction pressure of 150 MPa and a high rotation speed of 1500 rpm, and investigated the microstructural and mechanical-property inhomogeneity at the weld interface. X. Li et al. [11] fabricated FW joints of Ti64 and SUS321 stainless steel at 150 MPa with high rotation speeds ranging from 400 rpm to 1800 rpm, and examined the effect of the rotation speed on the joints’ microstructure and mechanical properties. The low friction pressure and high rotation speed can cause several issues. A low friction pressure will lead to a high welding temperature during the FW, causing a thick IMC layer formation [10,11]. This is because the temperature is required to be high enough to soften the interface materials so that they can be deformed to form the joint under such a low pressure. These findings have been reported for linear friction welding (LFW) studies and FW in our previous works [[16], [17], [18]]. On the other hand, a high rotation speed will make the peripheral velocity and temperature rising rate much higher at the weld interface periphery compared to those at the center, making it difficult to achieve a homogeneous temperature distribution and microstructural formation over the weld interface [10,11]. Furthermore, it has been claimed that the high temperature rising rate and the high peripheral velocity corresponding to the high shear strain rate between faying surfaces of both materials are key factors to cause the formation of harmful “mechanically mixed layers” and associated cracks/voids at the weld interface, which significantly deteriorate the FW joint quality of Ti64 and SUS316L stainless steel (SUS316L) [16]. Therefore, in this study, high friction pressure and ultralow rotation speed were adopted to friction weld Ti64 and SUS316L. The weld interface microstructure and mechanical properties of the obtained joints were carefully investigated in order to obtain a sound joint of dissimilar Ti64 and SUS316L.

Section snippets

Experimental procedures

As received Ti64 and SUS316L rods of 100 mm long having a diameter of 10 mm were used as base materials (BM). The chemical compositions of both materials are listed in Table 1. Before welding, the faying surfaces of both materials were lathe machined and ultrasonically cleaned. They were subsequently friction welded under high friction pressures of 400–500 MPa and low rotation speeds of 40–300 rpm, then terminated at a constant burn-off length of 4 mm. The data of burn-off length versus time

Results and discussion

Fig. 1a shows SEM micrographs of the weld interface center and periphery of the joints fabricated at 500 MPa and various rotation speeds of 300 rpm, 100 rpm [16] and 40 rpm. All the weld interface centers have similar flat interface morphologies without visible cracks/voids, whereas the periphery show significantly different morphologies at different rotation speeds. At 300 rpm, lots of mechanically mixed layers accompanied with large cracks/voids distributed thoroughly are identified at the

Conclusions

In summary, contrary to the typical conditions, an ultralow rotation speed and appropriate high friction pressure were adopted to friction weld Ti64 and SUS316L. The ultralow rotation speed provided a low temperature rising rate and a low peripheral velocity corresponding to a low shear strain rate between faying surfaces at the weld interface periphery, hence suppressing the formation of harmful mechanically mixed layers and associated cracks/voids. The appropriate high friction pressure was

Originality statement

I write on behalf of myself and all co-authors to confirm that the results reported in the manuscript are original and neither the entire work, nor any of its parts have been previously published. The authors confirm that the article has not been submitted to peer review, nor has been accepted for publishing in another journal. The authors confirm that the research in their work is original, and that all the data given in the article are real and authentic. If necessary, the article can be

CRediT authorship contribution statement

Huihong Liu: Conceptualization, Investigation, Writing - original draft, Funding acquisition. Hidetoshi Fujii: Resources, Writing - review & editing, Supervision, Funding acquisition.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

The authors wish to acknowledge the financial support by JST-Mirai Program Grant Number JPMJMI19E5, JSPS KAKENHI Grant Numbers JP19H00826, JP18K14027, and JP20K05169 and an ISIJ Research Promotion Grant.

References (20)

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