Al Alloy Sheets & Plates for Military Bridging System
Aluminium alloys in the form of sheets, plates and extrusions are extensively used in the manufacture of military bridging system for the Indian Army. Such alloys must be weldable and must have a combination of desired strength and high stress corrosion cracking (SCC) resistance. Accordingly, the copper‐free, weldable Al‐Zn‐Mg based 7xxx series alloys are an obvious choice for such applications.
Technology Developed at DMRL
Suitable changes in composition such as maintaining specific Zn : Mg ratios and Zn + Mg contents, addition of suitable recrystallization inhibiting elements, and heat treatments involving overaging are made to substantially improve the SCC resistance of these alloys. The improvement in SCC resistance by overaging is always accompanied by a considerable decrease in the strength. A novel artificial aging heat treatment was, therefore, formulated in order to attain the desired strength, as well as high SCC resistance (indicated by a minimum electrical conductivity of 40 % IACS). A combination of the above metallurgical solutions is incorporated for manufacturing the alloy in various semi‐product forms for military bridging systems.
Tensile Properties of Indigenized Copper‐Free 7xxx‐T7x51 Alloy Sheets & Plates (without Novel Aging Treatment)
| Alloy & Temper | Electrical Conductivity (% IACS) | 0.2 % PS (MPa) | UTS (MPa) | % Elongation |
| 7xxx‐Tx51 t = 6 mm | 39.20 | 345‐350 | 385‐390 | 10‐11 |
| 7xxx‐Tx51 t = 20 mm | 39.40 | 320‐325 | 365‐370 | 16‐18 |
Tensile Properties of Indigenized Copper‐Free 7xxx‐T7x51 Alloy Sheets & Plates (with Novel Aging Treatment)
| Alloy & Temper | Electrical Conductivity (% IACS) | 0.2 % PS (MPa) | UTS (MPa) | % Elongation |
| 7xxx‐Tx51 t = 6 mm | 40.6 | 320‐345 | 375‐390 | 10‐13 |
| 7xxx‐Tx51 t = 20 mm | 40.2 | 315‐330 | 360‐375 | 14‐16 |
