India’s aluminium industry sits on the cusp of sweeping changes in the way the metal will be consumed in the future. With both demand and consumption of aluminium in positive territory, the time is now opportune for producers to move beyond their traditional strengths in electricals and building segments and shift gears to the emerging applications offered by the defence and aerospace domains. Aluminium is widely used in making various ammunition components, parts for missiles and missile batteries, tanks, and components used in spaceships and satellites. A growing number of emerging applications in both these sectors make aluminium the metal of choice in the future. Key policy interventions of the Indian government, particularly the ‘Make in India’ push for defence bears testimony to this increasing appeal for aluminium.
Developing Special Alloys for Defence Needs
Aluminium alloys requirements in the Indian defence sector are substantial. Many of the applications have traditionally used aluminium alloys with improved mechanical properties. Some of the emerging applications require innovating process capabilities and joining technologies along with vastly improved specific strength and fracture resistance. The crux is increasing the availability of high purity aluminium with state-of-the-art processing facilities and advanced centres for characterisation, testing and certification. An analysis of consumption patterns indicates that the greatest share goes to extrusions since they play a vital role in feeding the input materials in the form of rods, plates, profiles and seamless tubes for defence applications. Though India has more than 250 active extruders producing a variety of complex extrusions for building and other applications, only two or three private players are producing, in meagre quantities, the strategic high strength aluminium alloy extrusions for defence application. Production of high strength aluminium alloy extrusions is confined to government undertakings like Ordnance factories.
India is still dependent on other countries for sourcing high strength aluminium alloy extrusions for strategic applications. Aluminium alloys are classified into eight series based on the major alloy addition. For high strength aluminium, the preferred alloy addition is copper and sinc. The high strength in these alloys is achieved by solution treatment and ageing heat treatment. Such alloys find extensive applications in defence- some of the applications are ammunition hardware, missile, rockets and rocket launchers, military bridges and airdrop platforms, cartridge cases and military aircraft.
Challenges in the way of meeting defence demand and R&D focus
There is enough demand for quality aluminium alloys in India’s navy, defence and aerospace sectors. But, India’s aluminium makers lack innovative product design, design parameters conversion and integration. The players are unable to meet the domestic demand for aluminium as they are dogged by issues pertaining to the quality of alloys, impurity, texture, scratch freeness, aesthetics, level of hydrogen content and lack of focus towards commercialisation. A big gap exists between the producers and commercially available products in the world market- this is exemplified by the fact that a state controlled entity like Hindustan Aeronautics Ltd meets its entire requirement through imports.
The high strength aluminium alloys are used in the form sheet/plates, extrusion, forgings and rolled rings and the consumption pattern indicates that the maximum share goes to extrusions. The manufacturing technology of high strength aluminium alloys is highly demanding in terms of scientific know how and expertise compared to the production of commercial aluminium alloys. These alloys have a tendency to crack during DC casting especially for billet sizes exceeding 300 mm diameter. The success of production of high strength aluminium alloy is possible only when suitable technology is introduced. Product development being a dynamic initiative, the contemporary aluminium manufacturers in India must seek to leverage with the worldwide network. While scientists and engineers in developed countries are working towards development of new alloys for strategic applications to improve the performance of the end product, the research emphasis is lacking in India. Moving forward, the focus has to be on promoting research on nano-ceramic coatings for open moulds and refractories in aluminium production. High strength to weight ratio, excellent fatigue strength, fracture toughness, corrosion resistance and good workability makes aluminium an ideal material for defence applications. Aluminium alloys are used in defence in the form of sheet, forgings and extrusions.
Strategising for Aerospace applications
Use of aluminium alloys in Indian launch vehicles is mostly limited to four key alloys: AA2014, AA2219, AA6061 and AA7075. They are used in propellant tanks and structures interconnecting different stages and components. Aluminium–lithium alloys also have been the primary candidate materials for aircraft and aerospace structures as they provide maximum density reductions possible among all aluminium alloys. Further, they also exhibit superior high cycle fatigue and fatigue crack growth resistances and excellent fracture toughness at cryogenic temperatures. Though, the tonnage requirement for all these alloys is low at present, the scope of such requirements is to increase by several times in the coming few years. Release agents play an important role in metal production. The materials used in launched vehicles are of premium quality conforming to aerospace material specification (AMS), normally produced in exclusive facilities with selected raw materials, special processing methods and equipments, elaborated testing and qualification. Indigenously, there are major constraints in producing aerospace quality alloys in the areas of melting, degassing, filtering and casting. Indian players have achieved some measure of success in producing aerospace quality billets and slabs. The need, however, is to establish state-of-the-art techniques/facilities for inline refining like rotor degassing, Ceramic Foam Filtering (CFF) and automatic casting lines. As the requirement for aerospace alloys in India grows coupled with buoyant opportunities for exports, the Indian aluminium industry can seriously think of forging specific ventures for catering to aerospace requirements.