Dissimilar friction stir welding between 5052 aluminum alloy and

Dissimilar friction stir welding between 5052 aluminum alloy and

AZ31 magnesium alloy

YAN Yong(鄢 勇), ZHANG Da-tong(张大童), QIU Cheng(邱 诚), ZHANG Wen(张 文)

School of Mechanical and Automotive Engineering, South China University of Technology,

Guangzhou 510640, China

Received 23 September 2009; accepted 30 January 2010

Abstract: Dissimilar friction stir welding between 5052 Al alloy and AZ31 Mg alloy with the plate thickness of 6 mm was

investigated. Sound weld was obtained at rotation speed of 600 r/min and welding speed of 40 mm/min. Compared with the base

materials, the microstructure of the stir zone is greatly refined. Complex flow pattern characterized by intercalation lamellae is

formed in the stir zone. Microhardness measurement of the dissimilar welds presents an uneven distribution due to the complicated

microstructure of the weld, and the maximum value of microhardness in the stir zone is twice higher than that of the base materials.

The tensile fracture position locates at the advancing side (aluminum side), where the hardness distribution of weld shows a sharp

decrease from the stir zone to 5052 base material.

Key words: dissimilar friction stir welding; 5052 aluminum alloy; AZ31 magnesium alloy; microstructure evolution; mechanical

property

1 Introduction

Aluminum alloys are widely used in automotive,

aerospace and ship industries due to the combination of

mass reduction and high strength. Magnesium alloys are

also attractive in these fields due to their lower density

and high specific strength. Therefore, it can be expected

that the joining of aluminum alloys and magnesium

alloys needs to be solved in industrial application.

However, it is difficult to obtain sound dissimilar welds

of these two kinds of alloys through conventional fusion

welding techniques since large inter-metallic compounds,

which have a strong negative effect on the mechanical

properties of the weld, are easy to form in these

processes[1].

Friction stir welding (FSW), a solid-state welding

process patented by The Welding Institute (TWI) in

1991[2], is a potential candidate for the joining of

dissimilar materials due to the lower processing

temperature over conventional fusion welding[3].

Defect-free welds have now been made by FSW in the

joining of different Al alloys (e.g. Al 2024/Al 7075)[4−5],

Al/steel[6−7], Al/copper[8−9] and Al/Mg[3, 10−13]. For

Al/Mg dissimilar FSW, YAN et al[11] investigated the

microstructure of AZ31 Mg alloy and 1060 Al alloys,

and found that the complicated microstructure

characterized by the intercalation lamellae band was

formed during dissimilar FSW. SOMASEKHARAN et

al[12] reported that microhardness profiles exhibited

uneven distribution and suggested that the complexed

intercalation structures should be responsible for

microhardness distribution. SATO et al[3] investigated

the dissimilar welding of AZ31 Mg alloy and 1050 Al

alloy and attributed the intermetallic compound Al12Mg17

to the uneven microhardness profiles. Due to the

complicated flow mechanism during dissimilar FSW, the

mechanism of microstructure evolution is not fully

understood up to now. The present study concentrated on

the understanding of microstructure evolution and

mechanical properties of the dissimilar FSW between

5052 Al alloy and AZ31 Mg alloy.

2 Experimental

5052 aluminum alloy and AZ31 magnesium alloy

plates with thickness of 6 mm were used in the present

study, and the chemical compositions are listed in Table 1.

Foundation item: Project(B01B7070270) supported by the Scientific Research Foundation for the Returned Overseas Chinese Scholars, State Education

Ministry, China

Corresponding author: ZHANG Da-tong; Tel: +86-20-87112272; Fax: +86-20-87112111; E-mail: dtzhang@