Elsevier

Materials & Design

Volume 89, 5 January 2016, Pages 737-748
Materials & Design

State-of-the-art of extrusion welding and proposal of a method to evaluate quantitatively welding quality during three-dimensional extrusion process

https://doi.org/10.1016/j.matdes.2015.10.033Get rights and content

Highlights

  • Proposal of a method to evaluate quantitatively welding quality during the three-dimensional extrusion process

  • Proposal of a non-dimensional factor to describe the average welding quality on the entire welding plane

  • Investigation of the effects of ram speed and the height of welding chamber on welding quality

Abstract

Aluminum alloy profiles have been widely used in many fields and are attracting more and more attention now. However, for the hollow profiles, longitudinal welding lines occur inevitably and appear on the extruded profiles. Currently, most research in the literatures focuses on the two-dimensional extrusion welding process, which could not reflect the real formation process of a welding line and there are not effective method to evaluate the welding quality during extrusion process. The first part of this work reviews the-state-of-the-art of the extrusion welding in the current literatures. In the second part, a novel method is proposed to evaluate the welding quality during a three-dimensional extrusion process. This method extends the application of the current welding criterion from a two-dimensional extrusion process to a three-dimensional one. By simulating the transient extrusion process of an aluminum tube with Forge-3D, the proposed method is used to evaluate the welding quality of the extrusion process. Based on the method, the effects of extrusion speed and welding chamber on welding quality are investigated quantitatively. With the increasing extrusion speed or decreasing height of welding chamber, the welding quality is getting worse, which is identical to the experimental observations in other publications.

Introduction

In recent years, aluminum alloy profiles have been widely used in many fields, such as rail transport, aerospace, automobile, shipping, electric power, energy, construction industry, etc. thanks to their low density, good surface appearance, high specific strength and excellent corrosion resistance. Especially, aluminum alloy profiles are attracting more and more attention today with their developments in direction of large-scale, thin-walled and complex cross-sections (Fig. 1).

Currently, more than 90% of hollow aluminum profiles are produced by porthole dies. During the extrusion process, the preheated billet gets through the die forced by the movement of extrusion ram and is divided into several metal flows by the die bridges, then the metal streams rejoin in the welding chamber and weld together under high temperature and high pressure. As a result, longitudinal welding lines occur inevitably and appear on the extruded profile along extrusion direction. The formation of welding lines is a solid-state bonding process, along with the evolution of the material microstructure, such as recovery, recrystallization and grain growth [1]. Compared with other parts of a hollow aluminum profile, the mechanical properties near longitudinal welds are relatively poor. Therefore, damage often occurs firstly near the longitudinal welding lines [2]. Fig. 2 shows the hollow aluminum profiles with bad welding quality, where damages always occur during the burst test. Therefore, with the demand for large-scale, thin-walled aluminum profiles with complex cross-sections, the more the corresponding number of welding lines in the profile, the more the potential welding defects occur. Accordingly, it is urgent and significant to study the formation mechanism of extrusion welding lines and to assess the welding quality of longitudinal welding lines accurately. This work mainly includes two parts: the first one is about the state of the art and the development of the extrusion welding in the current literatures, while the second one is to put forward a method to evaluate quantitatively the welding quality during the three-dimensional extrusion process.

Section snippets

Current research on extrusion welding

It is difficult to directly monitor the actual formation process of welding lines through physical techniques, so the current research on extrusion welding mainly depends on the following three methods: theoretical analysis, physical simulation experiment and numerical simulation methods.

Further application of K criterion in three-dimensional extrusion process

To extend the application of weld criteria from one welding path to the whole welding plane, the calculation of weld strength must consider all the possible weld paths on welding plane that contribute to welding quality, rather than only one welding path, which refers to the integral of all the p/σ value of welding points within the whole welding plane. According to the mathematical description of integral expression, K value can be described by the volume of the three-dimensional space as

Effect of extrusion speed on welding quality

In order to quantify the effect of extrusion ram speed on welding quality, the extrusion processes of the tube with different ram speeds are simulated. For each FE model, the average K value is calculated by taking into account at least five simulation steps at steady extrusion stage, as shown in Table 2. Though there is no obvious change among the K values at different ram speeds, the K value shows a downward trend with the increasing ram speed, which is in accordance with Valberg [38] and

Conclusions

In this work, a novel method is proposed to evaluate quantitatively the welding quality during a three-dimensional extrusion process by combining Forge-3D and Pressure–Time-Flow criterion (K criterion). Based on the proposed method, the effects of extrusion speed and welding chamber on welding quality are investigated and the following conclusions are drawn.

  • (1)

    The welding quality during a three-dimensional tube extrusion process is evaluated quantitatively. Different from the two-dimensional cases

Acknowledgments

The authors would like to acknowledge financial support from the National Natural Science Foundation of China (51575315 and 51375270) and Fundamental Research Funds of Shandong University (2015WLJH29).

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