Processing of Aircraft metals for service in severe conditions

Chrome-Nickel-Iron super alloys Inconel grades are the corrosion resistant metals. The anticorrosive degree of these materials is determined by the surface condition of metal and composition, temperature and concentration of the corrosive agent. They are commonly used in aerospace industry.

Inconel alloys closely resemble stainless steel in appearance. They are used in aircraft exhaust systems. Corrosion resistance of Inconel 625 is excellent against salt water and it can withstand temperatures of 1600oF. Inconel can be easily welded and has good working features.

Many aircrafts require in excess of this metal for use in multiple of vital sports. In choosing the suitable metals for the repair and maintenance of aircraft, it is essential to evaluate the structural repair manual. Aircraft manufacturers design structural members to meet the specific load requirement for a specific aircraft.

Four factors should be considered while choosing the aircraft materials: 1. maintain the structure strength. 2. Maintain aerodynamics 3. Maintain weight 4. Maintain the corrosion resistance properties

Different metal working processes of Inconel 600 and other grades are hot working, cold working and extruding. The method used is based on the metal used and the component needed, however in some cases hot and cold working methods can be together used to make a single component.

Hot working

Almost every corrosion resistant grade is hot worked from ingot into some form from which it is hot or cold processed to the final shape. When an ingot is stripped from its mold, the surface becomes solid however the inner surface is still molten. The ingot is then kept in a soaking pit that prevents loss of heat and the molten interior gradually solidifies. Subsequent to soaking, the temperature is equalized across the ingot, thereafter it is reduced to moderate size by rolling, making it more easily handled.

The billets are heated above the critical temperature and rolled into differ shapes of uniform cross section. Common rolled shapes of Inconel 718 are sheet, bar, etc. Hot rolled material is frequently finished by cold rolling or drawing to receive right finish dimensions and a bright smooth surface.

Complicated sections that cannot be rolled or areas of which only a small magnitude is needed, are commonly forged. Steel forging is a mechanical processing at temperatures more than the critical range to shape the metal as required. Forging is done by pressing or hammering the heated steel as long as the required shape is received.

Pressing is used when the forging parts are large and heavy, this process replaces hammering where high grade steel is needed. A press is slow acting, its force is uniformly sent to the center of the section, hence influencing the interior grain structure and exterior to receive the best feasible structure. Hammering can be used on relatively small pieces. As hammering transmits its force almost fast, its effect is confined to a small depth. So, it is essential to use a heavy hammer or to expose the part to the repeated blows to ensure complete working of the section. if the applied force is very low to reach the center, the finished forged surface will be concave. If the center was treated appropriately, the surface will be convex. The benefit of hammering is that the operator gets full control on the magnitude of pressing applied and the eventual temperature, and becomes able to develop small components of the high grade This forging is often recommended as smith forging. It is widely used where only a small count of parts are required. Significant machining time and material are saved when a component is smith forged to almost the finished shape.

Steel is usually harder than required and very brittle for practical implications when put under extreme internal strain. To relive strain and decrease brittleness, it is tempered after being hardened. It comprises of heating the steel in a furnace to a specific temperature and then cooling it in air or a special solution. Sometimes these alloys become very hard for forming and need re- processing or annealing.

Author Bio :

A metal lover who loves to talk about metals. I believe that metals are one of the most blissful thing on earth which can be used in many industrial applications.