Page 9 - Jan-Feb 2018
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of the tubes by restricting the process  process parameters and quality                 3.0 mm thick DMR291A-H24 sheet
to three-step drawing operations         control procedures for the production            produced at Hindalco, Hirakud
without the need of an intermediate      of slabs and heat treated sheets of the
annealing treatment, and a suitable      alloy having the desired dimensions           0.9 mm thick DMR291A-H24 sheet
annealing cycle for the resultant        and mechanical properties.                      produced at Hindalco, Hirakud
straight tubes to be heat treated
subsequently to the O temper. The        Naval Warship                             production processes and the quality
resultant annealed straight tubes                                                  control procedures of the indigenised
were then subjected to chemical,            Aluminium-magnesium based              materials (named DMR291A) were
dimensional, tensile and hundred per     alloys are widely used for the            approved by QAE(N), Kolkata and
cent non-destructive tests.              manufacture of superstructure of          Directorate of Naval Architecture
                                         naval warship. DMRL provided              (DNA), New Delhi.
   The straight tubes were subjected     crucial metallurgical inputs to reduce,
to the required bending operation        the loss of magnesium during melting         The competent authority in Indian
(as per the design) at M/s Autoforms,    and casting, hydrogen content in          navy approved the indigenised
Mumbai. The bent tubes were then         the molten metal prior to casting,        DMR291A sheets and plates for
heat treated to the peak aged temper at  and rejections at various stages          their use in superstructures in naval
M/s L&T, Coimbatore. The mechanical      of production processes through           warships in February, 2014. The Naval
properties, dimensional tolerances,      control on rolling and heat treatment     Construction Document (NCD)
shape, etc. have been verified and the   parameters for the production of          for these materials was issued by
process has been fully established.      sheets and plates of various thicknesses
                                         (up to 30 mm) and desired tempers
New Generation Anti-                     (H24 and M) at BALCO, Korba.
Radiation Missile
(NGARM)                                     The resultant materials met all
                                         the targeted properties, as inspected
   Aluminium alloy AA6061 sheets         by Quality Assurance Establishment
having thickness of 2.4 mm and heat      (Naval), [QAE(N)], Kolkata. Other
treated to annealed (O) and peak         properties such as corrosion resistance
aged (T6) tempers were produced at       (i.e., exfoliation corrosion resistance
BALCO, Korba for the manufacture         and stress corrosion cracking
of air frame components of NGARM.        resistance) and weldability were
DMRL provided all the necessary          evaluated in Central Electro Chemical
metallurgical inputs in terms of         Research Institute (CECRI), Karaikudi
                                         and Welding Research Institute
                                         (WRI), Trichy, respectively. The

Indigenised Al-Mg alloy DMR291A in the form of (a) as-cast ingots, (b) M plate (t = 25 mm),
                       and (c) H24 sheets (t=2 mm) produced at BALCO, Korba

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