Stainless and Aluminum for Aerospace Metal-to-Metal Bonding
In the 1890s, aluminum debuted in the burgeoning aerospace field. Count Ferdinand von Zeppelin’s eponymous rigid airship featured an internal aluminum structure. Even the Wright Brothers, intrigued by aluminum’s strength-to-weight ratio, used the lower-density alloy. Today, aerospace applications use stainless and aluminum for aerospace metal-to-metal bonding.
Metal-to-metal bonding uses adhesives or welding to join metals in creating aerospace structural parts. In aviation and space flight, vehicles endure severe temperature fluctuations, extreme pressure, and force. Your choice of stainless and aluminum for aerospace metal-to-metal bonding must account for these factors.
Aluminum combines easily with other elements, resulting in a compound called an alloy. Pure lightweight aluminum is very strong, and its alloys improve upon certain base qualities. For example, the mix of molten aluminum with magnesium, zinc, silicon, or copper can increase the material’s strength, electrical conductivity, or flexibility.
In 1954, the Aluminum Association established a method for naming alloys—or grades—using a four-digit code. The first digit represents the primary element used in the alloy. For instance, aluminum grades beginning with 2 refer to a copper-aluminum alloy. The digit 6 indicates a magnesium and silicon combination, magnesium-silicide. And 7 refers to zinc.
Aluminum alloys beginning with 2, 6, and 7 demonstrate characteristics necessary for aerospace applications.
Aluminum alloy 2024: The combination of high strength and fatigue resistance makes it ideal for applications requiring a high strength-to-weight ratio, like wings or fuselage.
Aluminum alloy 6061: A common aircraft aluminum, 6061 features easy machinability and welding for metal-to-metal bonding applications, plus a range of mechanical properties and good corrosion resistance.
Aluminum alloy 7050: High corrosion resistance and strength create high resistance to fractures, good for wing skins and fuselage.
Aluminum alloy 7075: One of the highest strength aluminum alloys, it has high levels of zinc, which gives it strength comparable to steel. Fatigue resistance and machinability make it a good choice for mechanical or adhesive metal-to-metal bonding applications.
Stainless steel is an iron-based grade of steel that contains between 10.5 and 30 percent chromium. Chromium interacts with oxygen to form a passive layer of chromium oxide that resists rust.
Like aluminum alloys, stainless steel alloys have numerical designations but with two different systems. The newer Unified Numbering System was co-developed by the Society of Automotive Engineers and the American Society for Testing and Materials. Five digits indicate an alloy’s composition. The prefix letter S designates a stainless-steel alloy.
The Society of Automotive Engineers also created the traditional three-digit naming system.
The 300 series of stainless is most common in aerospace applications and comprises austenitic grades. Austenitic alloys contain a minimum of 16 percent chromium.
Some high-chromium stainless steel alloys contain at least 8 percent nickel to improve corrosion prevention. The passive layer of these alloys also increases heat resistance.
Stainless steels contain less than 1.2 percent carbon, and L-designated grades have even less. Lower carbon content improves weldability, preferable for bonding methods that involve heat, such as welding. Higher carbon content in stainless steel results in a greater propensity for corrosion and brittle welds.
Between 426 and 750 degrees Celsius, chromium and carbon elements combine to form chromium carbides. This phenomenon is known as carbide precipitation, and it turns the metal either black, dark blue, or purple. Plus, the metal becomes severely weakened.
Clearly, there are a wide array of choices in stainless and aluminum for aerospace metal-to-metal bonding. Your project will dictate which metal works best. Iron-based metal such as stainless tends to be more versatile.
Certain aluminum alloys may lose mechanical properties such as strength and hardness during torch welding, which uses an open flame to melt and unite metals. By contrast, low-carbon stainless steels (those with the L designation) generally possess good weldability.
Aluminum alloys in the 6000 series perform well with laser-beam welding, especially when combined with a filler metal to help sensitivity to cracking. Laser-beam welding uses a beam to concentrate heat.
Electric arc welding uses an electric arc to concentrate heat, melt, and join metals. A common technique used in the aerospace industry, electric arc welding works for many stainless steel and aluminum alloys. However, high-strength aluminum alloys such as 7050 can crack under arc welding.
Friction welding generates heat by rubbing the surfaces to be joined at high speed. Friction welding occurs below the materials’ melting points. Thus, it can join all series of aluminum alloys, stainless steel, and dissimilar metals.
Structural adhesives connect metal surfaces with strong, flexible chemical bonds that also serve as sealants. Adhesives work well for dissimilar metals, and modern aerospace adhesives rival welding in their strength.
However, the structural adhesive takes time to cure, or harden. This can cause delays in the manufacturing process. Furthermore, the use of a metal adhesive may require additional surface preparation for your choice of alloy.
Due to supply chain interruptions, materials are scarce in North America. Yet Diversified Specialty Metals has a full stock of stainless and aluminum for aerospace metal-to-metal bonding.
Diversified Specialty Metals doesn’t rely on third-party logistics companies to deliver your materials. Instead, we own a full line fleet of trucks and tractor-trailers. As a result, we can fulfill your orders with a very short turnaround, even same day for customers in Quebec and Ontario.
Diversified Specialty Metals works closely with you and our suppliers to keep your inventory at optimal levels. That means we can align our raw material orders from suppliers directly with your production schedules.
Diversified Specialty Metals is one of the few companies in Canada with an AS9120B certification, quality management regulations specifically geared for aviation, space, and defense distributors.
The AS9120B certification ensures that Diversified Specialty Metals is meeting high standards in
product and service conformity;
on-time delivery;
counterfeit parts prevention;
human factors in maintaining and promoting quality;
configuration management, which ensures the quality of component products; and
ongoing third-party audits to evaluate compliance.
Diversified Specialty Metals offers a full catalog of stainless and aluminum for aerospace metal-to-metal bonding. Our alloys respond well to adhesives and welding. We can deliver the materials you need quickly, at the highest quality.
Check out our vast inventory of aerospace-grade materials, and get your quote today.
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