Formation And Distribution of Brittle Structures in Friction Stir Welding of AA 6061 To Copper

Page 1

Mechanics, Materials Science & Engineering, May 2016

ISSN 2412-5954

Formation And Distribution of Brittle Structures in Friction Stir Welding of AA 6061 To Copper. Influence of Preheat Seyed Vahid Safi1,a, Hossein Amirabadi2, Mohammad Kazem Besharati Givi3 1

M.Sc. student. Mech. Eng., University of Birjand, Birjand, Iran

2

Assoc. prof., Mech. Eng., University of Birjand, Birjand, Iran

3

Assoc. prof., Mech. Eng., University of Tehran, Tehran, Iran

a

vahid.safi@gmail.com DOI 10.13140/RG.2.1.2620.9684

Keywords: friction stir welding, mechanical properties, preheat, intermetallic.

ABSTRACT. In this paper, apart from introducing brand new warm friction stir welding (WFSW) method, the effect of preheating on friction stir welded of copper and aluminum alloys sheets and its influence on improving the mechanical properties of the weld were investigated. Sheets of aluminum alloy 6061 and copper with thickness of 5mm were used. The tool was made of tool steel of grade H13 with a threaded cone shape. Rotational speeds ( ) of 1200-1400 rpm and traverse speeds ( ) of 50-100 mm/min were used for better understanding the behavior of the tools during the heat input. and micro hardness tests were done to compare the mechanical properties of the welds. Considering to the high thermal conductivity of both copper and aluminum, the reason of increase in strength of the joints could be related to the low temperature gradient between the weld zone and base metal because the heat gets out of the stir zone with lower steep. A significant increase in hardness is observed in the SZ for the following reasons: (i) the presence of concentric grains with intensely refined recrystallization and (ii) the presence of intermetallic compounds. The tensile test results showed 85% 1200 rpm and traverse speed of 50 mm/min. In the present study, intermetallic compounds and the precipitates are moved to the grain boundaries during the welding process. These precipitates act as strong obstacles to the movements of dislocations and increase the deformation resistance of material. This phenomenon may result in locking of grain boundaries and consequently decrease of grain size. This grain refinement can improve the mechanical properties of welds. Accordingly, hardness and strength of the material will be increased.

1. Introduction. FSW is a process including many actions and interactions between a series of simultaneous thermodynamic processes. These reactions are the results of heat input rate, cooling rate, flow and deformation, dynamic recrystallization and integration of mechanical joints [1].This method of welding was invented in 1991 by Thomas Wayne et al. in TWI in Cambridge, England [2].FSW is a relatively new method in metal joining that because of solid state nature of this method (no melting happens at joining) it has some advantages comparing with other fusion welding methods. Low distortion and shrinkage, good mechanical properties, fewer defects and the ability of welding some metals that cannot be welded with fusion welding methods are among the most important advantages of this method [3]. In last few years, this process has been used in aerospace and aviation industries, automotive industries, fuel tanks etc. in most developed countries. During this process, imposes high lateral forces to the material during deformation which causes temperature to increase up to about 70-80% of its melting temperature [4, 5].Copper has a wide range of applications because of its great thermal and electrical conductivity, corrosion and fatigue resistance and good flexibility. Copper alloys have various set of properties, which is dependent on the addition of elements and heat treatment [6]. Today, aluminum and its alloys have a wide range of applications in defense industry, aerospace, transportation, marine industry, construction industry, packaging and containers etc. some of the properties which made aluminum and its alloys as one of the most economical and popular group of MMSE Journal. Open Access www.mmse.xyz

25


Turn static files into dynamic content formats.

Create a flipbook
Issuu converts static files into: digital portfolios, online yearbooks, online catalogs, digital photo albums and more. Sign up and create your flipbook.