Experimental Investigation of Dry and Cryogenic Friction Stir Welding of AA7075 Aluminium Alloy

A Praveen Raj Navukkarasan,C Chandrasekhara Sastry,M A Muthu Manickam,K Shanmuga Sundaram,Gianfranco Palumbo

doi:10.1155/2021/9961590

Abstract

An attempt has been made to investigate dry and cryogenic friction stir welding of AA 7075 aluminium alloy, which is predominantly availed in aerospace and defence component industries. These industries avail friction stir welding for joining two nonferrous materials, and minimal deviations and maximum strength are the preliminary and long time goal. A cryogenic friction stir welding setup was developed to conduct the joining of two aluminium alloy pipes. An increase of 0.76–42.93% and 3.79–31.24% in microhardness and tensile strength, respectively, is ascertained in cryogenic friction stir welding in correlation to dry friction stir welding of aluminium alloys. TOPSIS evaluation for the experimental run indicated tool profile stepped type, pipe rotation speed of 1000 rpm, welding speed of 50 mm/min, and axial force of 8 kN as close to unity ideal solution for dry and cryogenic friction stir welding of AA 7075 aluminium alloys. The friction stir-welded component under the cryogenic environment showcased drop in temperature, curtailed surface roughness, and fine grain structure owing to reduction in temperature differential occurring at the weld zone. A curtailment of 50.84% is ascertained in the roughness value for cryogenic friction stir welding in correlation to dry friction stir welding of AA 7075 alloy. A decrement of 21.68% is observed in the grain size in the cryogenic condition with correlation to the dry FSW process, indicating a drop in the coarse structure. With the curtailment of grain size and drop in temperature differential, compressive residual factor and corrosion resistance attenuated by 40.14% and 67.17% in the cryogenic FSW process in correlation to the dry FSW process, respectively.

Highlights

IntroductionAluminium alloy 7075 has been extensively availed in the areas of military vehicle armour materials, Earth excavating machines, bridges, aerospace components, and majority of the defence high-stressed applications [1]. e salient importance of this material is limited due to its welding properties as the fusion problem is predominant in 7075 aluminium series, i.e., porosity formation, solidification of hot cracked areas in the welded zone, and increase in the microfissuring aspect in the semipartially melted zone (SPMZ) [2,3,4,5,6,7]. e composition of AA 7075 aluminium alloy possesses copper, which does not have a specific melting point, and this creates a wide melting range for the alloy with a very low solidus temperature making it susceptible to hot cracks (welded zone) during fusion welding [1, 5, 8]
A curtailment of 50.84% is ascertained in the roughness value in cryogenic friction stir welding in correlation to dry friction stir welding of AA 7075 alloy. e surface roughness decrease can be attributed to the curtailment of the heat affected zone (HAZ) zone, as decrease in the roughness parameter is dependent on the temperature differential drop [24]
It is found that the compressive residual factor increases by 40.14% in cryogenic friction stir welding in correlation to dry friction stir welding of AA7075 aluminium alloy. e attenuation in the residual factor indicates higher weld life integrity manufactured under cryogenic conditions

Summary

Introduction

Aluminium alloy 7075 has been extensively availed in the areas of military vehicle armour materials, Earth excavating machines, bridges, aerospace components, and majority of the defence high-stressed applications [1]. e salient importance of this material is limited due to its welding properties as the fusion problem is predominant in 7075 aluminium series, i.e., porosity formation, solidification of hot cracked areas in the welded zone, and increase in the microfissuring aspect in the semipartially melted zone (SPMZ) [2,3,4,5,6,7]. e composition of AA 7075 aluminium alloy possesses copper, which does not have a specific melting point, and this creates a wide melting range for the alloy with a very low solidus temperature making it susceptible to hot cracks (welded zone) during fusion welding [1, 5, 8]. Major benefits of availing the FSW process is (i) limited weld defects, (ii) addressing aluminium welding capability (difficult to weld material classification for aluminium), and (iii) way better dimensional capability if the process occurs in a controlled manner. All these above are specific to FSW if the whole process is well maintained and run in an optimized condition [3,4,5,6,7,8, 10]. In this method of joining materials, a nonconsumable tool pin profile generates friction heat by rotating between the parent material, as indicated in Figure 1. e rotation of the tool ensures proper stirring effect and mixing of the materials in and around the tool pin; with a combination of mechanical and thermal treatment, the welding process is completed [3,4,5,6,7, 9, 11]

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Results

Conclusion