The Paton Welding Journal, 2014, №04



2014 №04 (08)

DOI of Article 10.15407/tpwj2014.04.01

2014 №04 (02)

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The Paton Welding Journal, 2014, #4, 6-16 pages

STRUCTURAL FEATURES OF FSW JOINTS OF METALS WITH DIFFERENT ELEMENT SOLUBILITY IN THE SOLID PHASE

G.M. GRIGORENKO, L.I. ADEEVA, A.Yu. TUNIK, S.N. STEPANYUK, M.A. POLESHCHUK and E.V. ZELENIN

E.O. Paton Electric Welding Institute, NASU. 11 Bozhenko Str., 03680, Kiev, Ukraine. E-mail: office@paton.kiev.ua
 
 
Abstract
Results of investigation of the structure and properties of dissimilar metal joints made by friction stir welding (FSW) are given. Systems with unlimited (Ni-Cu) and limited (Cu-Fe) solubility, as well as absence of component solubility (Al-Fe) in the solid state were studied. FSW of copper and nickel produced a sound welded joint with metal interpenetration to 3 mm depth. Mechanical mixing of metals plays the leading role in this process, whereas diffusion processes are negligible. Structure refinement occurs in mechanical mixing bands as a result of recrystallization processes. Copper diffusion into nickel along grain boundaries proceeds down to 20 mm depth with formation of interlayers of these metals solid solution. When studying the copper to steel welded joint, it was established that metal mixing has a leading role also in this process, and the role of diffusion processes is small. During welding a considerable grain refinement takes place both in the recrystallization zone, and in thermomechanically affected and heat affected zones. FSW of aluminium to iron resulted in formation of the joint zone of a considerable volume with aluminium penetration into iron down to 2.5 mm depth. Metal interaction proceeds here, namely mass transfer, primarily, of aluminum, and subsequent formation of Fe2Al7, FeAl2 compounds. The hardest regions of welded joint zone contain intermetallics in the aluminium matrix. Such a structure has the hardness of 2870 С 410 MPa that is more than 3 times lower than that of iron aluminides Results of the conducted investigations allow recommending this welding process to produce bimetal joints of dissimilar metals with different solubility of elements in the solid state. 20 Ref., 5 Tables, 15 Figures.
 
 
Keywords: friction stir welding, welded joint, bimetal mechanical mixing of metals, diffusion, solid phase solubility, microstructure, X-ray microprobe analysis, elemental composition, microhardness
 
 
Received:                02.10.13
Published:               28.04.14
 
 
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