O. Jensrud, J. I. Moe, SINTEF Raufoss Manufacturing AS, Raufoss, Norway
The improvement of lightweight aerospace components indeed requires new development of the aluminium alloy used. The challenges in applying high strength aluminium alloys are corrosion resistance and ductility in the temper of maximum strength. In addition have an alloy suitable for plastic forming to manufacture semi parts, in the Raufoss case small rocket engines. The main idea of the new development has been reduction of the elements Cu and Fe in comparison with older alloys like AA7278 and AA7050. It is strongly believed that constituents of AlCuFe play and key factor in corrosion behaviour and especially for anodised qualities. It is also known that addition of Zn gives rather high level of strength in hardened tempers without reduction of formability. The new alloy introduced in small rocket engines has higher Zn and lower Cu content compared with older qualified materials. In addition to chemical composition the microstructure in the final temper are as important as chemistry and especially the grain structure. To control grain structure during processing of the material from ingot casting to final shape and temper the elements Zr and Cr play an important role in combination with an exact defined thermo mechanical route. The microstructure controls the most severe corrosion phenomena’s like stress corrosion and grain boundary attacks.
The new alloy (Al+Zn8.8+Mg2.8+Cu0.5+Zr0.15+Cr0.18) gives a yields strength of 630MPa with an elongation of 10% for a cold extruded and heat treated tubular part.
The introduction of the new Raufoss Alloy RA7090 in the rocket motor engine has improved the performance of the Raufoss Nammo AS rocket system. The main improvements are corrosion resistance, better ductility as well as a significantly easier manufacturing chain from molten alloy to final engines.
An concluding a better performance of the rocket engine system.
Summary: The improvement of lightweight aerospace components indeed requires new development of the aluminium alloy used. The challenges in applying high strength aluminium alloys are corrosion resistance and ductility in the temper of maximum strength. In addition have an alloy suitable for plastic forming to manufacture semi parts, in the Raufoss case small rocket engines.
The main idea of the new development has been reduction of the elements Cu and Fe in comparison with older alloys like AA7278 and AA7050. It is strongly believed that constituents of AlCuFe play and key factor in corrosion behaviour and especially for anodised qualities. It is also known that addition of Zn gives rather high level of strength in hardened tempers without reduction of formability. The new alloy introduced in small rocket engines has higher Zn and lower Cu content compared with older qualified materials. In addition to chemical composition the microstructure in the final temper are as important as chemistry and especially the grain structure. To control grain structure during processing of the material from ingot casting to final shape and temper the elements Zr and Cr play an important role in combination with an exact defined thermo mechanical route. The microstructure controls the most severe corrosion phenomena’s like stress corrosion and grain boundary attacks.
The new alloy (Al+Zn8.8+Mg2.8+Cu0.5+Zr0.15+Cr0.18) gives a yields strength of 630MPa with an elongation of 10% for a cold extruded and heat treated tubular part.
The introduction of the new Raufoss Alloy RA7090 in the rocket motor engine has improved the performance of the Raufoss Nammo AS rocket system. The improvements are corrosion resistance, better ductility as well as a significantly easier manufacturing chain from molten alloy to final engines.
