383 Trends in aluminium alloy development and their joining methods l  SeP]RTS EcdSh T]cTa A% "cS% Rev. Adv. Mater. Sci. 44 (2016) 383-397 Corresponding author: Paul Kah, e-mail: paul.kah@lut.fi TRENDS IN ALUMINIUM ALLOY DEVELOPMENT AND THEIR JOINING METHODS Richard Rajan, Paul Kah, Belinga Mvola and Jukka Martikainen Laboratory of Welding Technology, Lappeenranta University of Technology, P.O. Box 20, FI-53851, Lappeenranta Finland Received: July 10, 2015 Abstract. The growing concerns on issue of energy saving and environmental conservations has considerably increased the demand for lightweight structures in automobile, aerospace and marine industries. Aircraft manufacturers adhere to the life cycle approach for selection of mate- rials as cost reduction has become the main criteria in many airlines. Aluminium alloys have been the primary material choice in the structural parts of aerospace and marine sectors for more than 80 years. Although modern composites, due to their excellent fatigue strength, corro- sion resistance, reduced weight and high specific properties, appears to be a tempting replace- ment for aluminium alloys; its higher initial cost and expensive maintenance limits its wide- spread usage in airframe construction. Among the high performance materials, Aluminium is a low cost and easily produced metal that can relatively be subjected to high levels of stresses. Nowadays highly customized aluminium alloys are developed to meet the requirements of aero- space industries, which can effectively compete with composite materials. Increasing applica- tion of aluminium in various industrial sectors is the main driving force for technologists to develop a viable and efficient technology for joining aluminium alloys. These developments avoid adverse effects of welding on the mechanical, chemical and metallurgical properties of aluminium alloys desired for longer life. The main objective of this article is to explore the devel- opment and usage of aluminium alloys in aerospace industries. The improvements in the me- chanical properties of the Al-Cu (2xxx series), Al-Zn (7xxx series), and Al-Li alloys have been discussed and compared. Additionally, a critical review of the advancements in joining methods of aluminium alloys has been performed. 1. INTRODUCTION Energy efficiency has become top priority of national and international policies. Excessive energy con- sumption in the past has resulted in significant rise in CO 2 levels and thus major climate changes. Also, the airlines are concerned with energy consump- tion due to the significant rise in fuel cost. Therefore aircraft manufacturers are obliged to address both, the concerns of government to minimize ecological X?_PRc Pb fT[[ Pb cWT PXa[X]Tqb ST?P]S UAa UdT[ TUUX cient aircraft. In these continuously changing eco- nomic times, aircraft manufacturers are on a con- stant quest for finding ways to reduce the fuel con- sumption of aircrafts. The best way to reduce the weight of the aircraft is through incorporating lighter materials that results in reduced fuel consumption. The continuous aging of the civil and military air- craft creates a demand for aircraft that fly beyond their original design lives. This poses different prob- [T?b# X]R[dSX]V cWT P4X[Xch AU PXaRaPUcqb ?PcTaXP[ cA maintain damage tolerance [1]. The structural in- tegrity of the aircraft is threatened by the simulta- neous presence of fatigue and/or corrosion at mul- tiple locations and this is termed as Multi-site dam- age (MSD) [2]. One of the major causes for most