When manufacturing aircraft, heat treating metals is a required step of the process. Through such treatments, metal components can have their strength increased to withstand the amount of stress that they are subjected to during a standard flight operation. From aircraft landing gear to the aircraft bulkhead, a great number of parts and structures are heat treated to achieve better strength and performance. In this blog, we will provide an overview of aircraft component heat treatment, allowing you to understand how it is carried out and how it benefits aerospace applications.
In the present, aluminum material remains the most widely used for aircraft construction. This is due to the fact that it presents high strength to weight ratios, those of which are highly beneficial for heavier-than-air flight. With heat treatment, aluminum can attain high strength to excel in extreme environments, all while remaining relatively low in cost. For the construction of aircraft, aluminum alloy grades such as 7040, 7050, and 7075 serve as the most popular due to their high corrosion resistances and ability to be heat treated. Depending on whether the structure is the aircraft bulkhead, skin, or other fuselage components, different grades can present varying attributes to cater towards a specific need.
Generally speaking, aluminum alloys are defined as heat treatable if the alloy responds to precipitation hardening. Precipitation hardening is a special technique used during heat treatment, and it refers to the reheating of the metal following an annealing or austenite conditioning procedure and quench. While this procedure increases the strength of the given alloy steel, it can also make machining the component much easier. By enacting controlled precipitation of solutes and managing temperatures, the mechanical and corrosive properties of the alloys can be manipulated to serve a given application or environment. Temperature control is also crucial for the safety of the components, as the heat required for heat treatment is often extremely close to the eutectic melting temperature.
To treat and quench alloys with a solution, many aerospace engineers will utilize large ovens that can reach extreme temperatures. In the case that a furnace is placed above the quench tank, the quench tank may be movable with a set of rails. There may also be more than one quench tank present for a given assembly, allowing for a number of quenchants to be used for the heat treatment of aluminum parts.
When conducting quenching for the heat treatment of aircraft components, it is important to understand the various effects that different operating values can have on the finalized product. Through changes in temperature, the diffusion rate can be changed. With higher temperatures, the diffusion rate is at its greatest. If the diffusion rate drops or there is low supersaturation, the rate of precipitation also remains low. Through the use of diagrams and charts created through studies, one can be provided the assistance needed to understand the temperatures and rates that affect precipitation, supersaturation, and diffusion.
While heat treating aircraft bulkheads, fuselage components, and other aircraft components can prove extremely useful for the production of aerospace parts with high strength, it is not without its possible mishaps. During the stages leading up into heat treatment, various operations may cause defects to occur. If the issue was a direct result of heat treating aluminum, it most likely occurred during the stage of solution heat treatment or quenching. During the heat treatment phase within a solution, the most common defects that may occur include under-heating, oxidation, or incipient melting. With quenching, on the other hand, slow quenching may cause various distortions and incorrect supersaturation.
With oxidation, heat treated components may begin to blister on their surfaces. This is typically the result of high temperature exposure over a long period, causing hydrogen from moisture to diffuse into the metal. To mitigate the effects of hydrogen blistering, removing moisture before heat treatment is highly recommended. Additionally, ammonium fluoroborate can also be used with certain aluminum alloys to deter the formation of blistering. As such materials are highly corrosive, any worker handling them should have the proper protective gear and equipment needed for safety. Ammonium fluoroborate is also very corrosive when exposed to high temperatures, and as such the furnace used for heat treatment should be manufactured from stainless steel to withstand the impact of the process.
Incipient melting refers to when certain sections of the alloy begin to melt before the rest of the component, often resulting in inadequate properties that are not equal throughout the metal. Oftentimes, such metals will be most affected in their tensile strength, toughness, and ductility. Typically, incipient melting is the result of localized solute concentrations or rapid heating of the component.
As a somewhat opposite issue, underheating can also be detrimental to alloys, causing solutes to incompletely solidify. As a result of such an occurrence, certain properties needed for a given application may not be attained. Because of this, the particular alloy could prove unusable for the assembly of the aircraft and its various structures.
During the quenching phase of heat treatment, distortion is the most widely faced issue by manufacturers. Generally, differential cooling and thermal strains can both affect the orientation of the particular part, as non-uniform heat transfer or cooling can cause distortion. As aluminum is highly susceptible to distortion as compared to other metals such as steel, the temperatures and rates of heat treatment need to be closely monitored and controlled throughout the process. By implementing racking or other supports, heat treatment can be conducted more efficiently to avoid distortion as much as possible. Nevertheless, some distorted components may be able to be straightened and still implemented on an aircraft.
Through the heat treatment of aluminum and other aircraft metal alloys, high strength to weight ratios can be achieved for efficient construction and operations. At Internet of Industrials, we are your sourcing solution for aircraft fuselage parts and more, offering competitive pricing on aircraft bulkhead parts, aircraft landing gear components, aircraft displays, and much more. Explore our expansive part listings at your leisure, and you may begin the purchasing process at any point through the submission of an Instant RFQ form. Get started today and see how we can fulfill all of your operational needs with ease at Internet of Industrials.
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