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Research Papers

Self-Piercing Riveting of Wrought Magnesium AZ31 Sheets

[+] Author and Article Information
J. W. Wang

Z. X. Liu1

Y. Shang, A. L. Liu, M. X. Wang, R. N. Sun

Key Lab of Material Physics, School of Physics Engineering,  Zhengzhou University, No. 75, Daxue Road, Zhengzhou, Henan Province 450052, China

Pei-Chung Wang

Manufacturing Systems Research Lab, General Motors Research and Development Center, 30500 Mound Road, Warren, MI 48090pei-chung.wang@gm.com

1

Corresponding author.

J. Manuf. Sci. Eng 133(3), 031009 (Jun 09, 2011) (9 pages) doi:10.1115/1.4004138 History: Received June 23, 2010; Revised April 03, 2011; Published June 09, 2011; Online June 09, 2011

The high strength-to-weight ratio of magnesium alloys makes them attractive for automotive applications. These materials have been used for the engine cradle, seat frame, and shock tower applications to reduce vehicle weight. Despite these advantages, there are limiting factors to the application of magnesium alloys. One of these factors is the joining of magnesium alloys. Although there are various joining processes available, self-piercing riveting (SPR) is particularly promising. It provides not only the speed but also the necessary structural strength. However, because of the large amount of deformation associated with the process and the limited formability of magnesium at room temperature, SPR often results in part cracking of the riveted magnesium alloys, which reduces the part quality. In this study, a method of preheating the magnesium alloy before riveting was adopted to improve the joint quality. The fabrication of the desired SPR joints was investigated as a function of the preheat temperature and strain rate. To determine the optimum preheat temperature, Zener–Hollomon parameter was employed. Experiments were conducted to validate the proposed preheat temperature. Magnesium alloy AZ31 with a thickness of 2 mm was preheated with various temperatures prior to self-piercing riveting. The appearances, cross-sections, and mechanical tests of the SPR magnesium AZ31 joints were investigated. It was found that a preheat temperature of 180–200°C largely eliminated the discrepancies in SPR 2 mm thick magnesium AZ31 joints. The joint strength increases with increasing preheat temperature from ambient to 200°C. The strength increase is attributed to the reduction in joint discrepancies and an increase in mechanical interlock between the rivet and work pieces. The current findings on the development of a method can be used to determine the preheat temperature for self-piercing riveting of magnesium castings.

Copyright © 2011 by American Society of Mechanical Engineers
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Figures

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Figure 1

Illustration of self-piercing riveting process

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Figure 2

Cross-section of a typical SPR Joint

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Figure 3

Configuration of a lap-shear SPR joint

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Figure 4

Effect of the delay time on the coupon temperature

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Figure 5

(a) Schematic of the cross-section of a riveted joint, (b) joint interlock, (c) the distance between the rivet foot and the outer surface of the bottom sheet, (d) the gap between the outer surface of the rivet body, (e) the gap between the joined sheets, and (f) cracks in the bottom sheet

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Figure 6

Appearance of SPR 2 mm thick magnesium AZ31 joint at ambient temperature

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Figure 7

Relation between riveting velocity and strain rate

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Figure 8

Effect of the temperature on the (a) stress–strain characteristics, (b) tensile strength, and (c) elongation of 2 mm thick wrought magnesium AZ31 alloys

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Figure 9

Fractured samples after Gleeble tests under various temperatures under a strain

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Figure 10

Effect of strain rate on the (a) stress–strain characteristics, (b) strength and (c) elongation of 2 mm thick wrought magnesium AZ31 alloy

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Figure 11

Effect of Zener–Hollomon parameter on the tensile strength and ductility of magnesium AZ31 alloy for temperatures 25, 150, 180, 200, and 230°C at each of the following strain rates 0.0013 s−1 , 1.7 s−1 , 4.1 s−1 , and 5 s−1

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Figure 12

Effects of the temperature and strain rate on the (a) strength and (b) elongation of 2 mm thick wrought magnesium AZ31 alloys

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Figure 13

Effect of preheat temperature on the appearance of self-piercing riveted 2 mm thick magnesium AZ31: (a) 150°C and (b) 180°C

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Figure 14

Sections of the joints riveted at various preheat temperatures: (a) ambient, (b) 150°C, (c) 180°C, and (d) 200°C

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Figure 15

Cracking emerged around the tails of the rivet (indicated by the cycle in Fig. 1) for the joints produced at various preheat temperatures at: (a) 150°C and (b) 180°C

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Figure 16

Effect of preheat temperature on the shear strength of the SPR joints

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Figure 17

Attributes of a SPR joint Δt1 , Δt2 : remaining material thickness of the bottom sheet, Δt3 : mechanical interlock distance between the rivet and workpieces

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Figure 18

Effect of preheat temperature on the predominant failure mode of SPR joints: (a) ambient temperature, (b) 150°C, and (c) 180°C

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Figure 19

Effect of the preheat temperature on the remaining material thickness of the bottom sheet (Δt1 , Δt2 ) and mechanical interlock distance (Δt3 )

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