FSW IN ALUMINIUM

Materials Science and Engineering A 496 (2008) 262–268

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Materials Science and Engineering A

journal homepage: www.elsevier.com/locate/msea

Effect of friction stir welding speed on the microstructure and mechanical

properties of a duplex stainless steel

T. Saeid, A. Abdollah-zadeh∗, H. Assadi, F. Malek Ghaini

Tarbiat Modares University, Department of Materials Engineering, P.O. Box 14115-143, Tehran, Iran

a r t i c l e i n f o

Article history:

Received 11 April 2008

Received in revised form 8 May 2008

Accepted 9 May 2008

Keywords:

Friction stir welding

Duplex stainless steel

Microstructure

Mechanical properties

a b s t r a c t

The present study focuses on the effect of the welding speed on the microstructure and mechanical

properties of the stir zone (SZ) in friction stir welding (FSW) of SAF 2205 duplex stainless steel. A single

tool, made of a WC-base material, was used to weld 2 mm-thick plates at a constant rotational speed

of 600 rpm. X-ray radiography revealed that sound welds were successfully obtained for the welding

speeds in the range of 50–200 mm/min, whereas a groove-like defect was formed at the higher speed

of 250 mm/min. Moreover, increasing the welding speed decreased the size of the ˛ and  grains in the

SZ, and hence, improved the mean hardness value and the tensile strength of the SZ. These results are

interpreted with respect to interplay between the welding speed and the peak temperature in FSW.

© 2008 Published by Elsevier B.V.

1. Introduction

Duplex stainless steels (DSS) containing both ferrite (˛) and

austenite () phases are increasingly used as alternatives to

austenitic, ferritic stainless steels and nickel-base alloys. They represent

an important and expanding class of steels with an attractive

combination of mechanical properties and corrosion resistance.

This is related to the fact that the microstructure of duplex stainless

steels allows a beneficial mixture of ˛ and  properties. High

strength and corrosion resistance come from the ferrite, whereas

the austenite phase influences ductility and resistance to uniform

corrosion [1–4].

In these materials, a good combination of properties is achieved

at an ˛/ ratio of approximately 1:1. However, due to melting and

rapid solidification in fusionwelding processes, this desired ratio is

upset. Also, precipitation of brittle intermetallic phases may occur.

In general, theweldmetal and the heat-affected zone of DSS exhibit

higher ferrite content, coarser grains and more extensive precipitation

of intermetallic phases than the base metal. All of these

factors have the tendency to reduce both the corrosion resistance

and the mechanical properties (mainly, ductility and toughness) of

the weldment [1,5–7].

To avoid problems associated with the fusionwelding processes

of DSS, solid-state joining technologies would appear to be more

∗ Corresponding author. Tel.: +98 21 88005040; fax: +98 21 88005040.

E-mail address: zadeh@modares.ac.ir (A. Abdollah-zadeh).

suitable. As a solid-state process, friction stir welding has attracted

considerable attention. It has been shown that, FSW can alleviate

most of the problems caused by the fusionwelding processes in carbon

steels having carbon contents up to 1.02 wt% [8–10],mild steels

[11], DH36 steel [12] and stainless steels [13–19]. Regarding to FSW

of duplex stainless steels, there have been few papers in the open

literature. For example, Okamoto and Hirano [18] conducted a feasibility

work and demonstrated that FSWoffers a sound weld joint

in a 6-mm thick 329 duplex stainless steel. The authors reported

an increase in austenite percentage from 43% in the parent material

to 56% in the weld zone. Sato et al. [19] conducted a detailed

examination of the microstructure and the mechanical properties

in the friction stir welding of SAF 2507 super duplex stainless steel

using PCBN tool. They found that FSWsignificantly refined the ferrite

and austenite phases through dynamic recrystallization. Based

on the obtained results, they concluded that the formation of ferrite

and austenite fine grains increase hardness and strength in the

stir zone.

These cited studies have yielded some important knowledge on

the microstructure and mechanical properties in FS-welded DSS.

The present work explores the problem further, through a detailed

study of the effect of the welding parameters on the weld thermal

cycle, microstructure and mechanical properties of the stir zone.

2. Experimental procedure

Bead-on-plate welding of a commercial SAF 2205 duplex stainless

steel was performed in the present study. The chemical

0921-5093/$ – see front matter © 2008 Published by Elsevier B.V.

doi:10.1016/j.msea.2008.05.025

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