Wednesday, April 18, 2012

Aluminium and Nickel Alloys

 Although many metals have useful characteristics, sometimes their intrinsic weaknesses (such as brittleness or susceptibility to oxidation) make them difficult to use in their pure form. However, alloying these metals with other substances can compensate for the base-metal’s weaknesses and enhance its innate strengths. Most metals, by the time they are ready to be worked and manufactured into an end-product, are no longer in their pure state but have been carefully turned into a metal alloy. Depending on the specific base metal, the processes used and substances added to turn a metal into an alloy can vary.

Aluminum Alloys

Aluminum alloys contain aluminum as the primary metal. Typically, aluminum alloys are used in applications where light-weight materials or corrosion-resistant materials are warranted. Alloying elements include copper, zinc, manganese and silicon, which can be combined with aluminum to produce two distinct categories of aluminum alloys: casting and wrought alloys.

Cast aluminum alloys typically have low melting points and tensile strength when compared to wrought aluminum; the most commonly used aluminum alloy is aluminum silicon, which features high levels of silicon that enable the alloy to be easily cast. Cast aluminum alloys are classified according to the Aluminum Association (AA) and divided into eight different groups. The first cast aluminum alloy series features alloys that are 99 percent aluminum, while the other series are divided according to main alloying element: lithium, copper, silicon, zinc and magnesium.

Wrought aluminum accounts for the majority of aluminum products, such as those manufactured from extrusion or rolling. Wrought aluminum alloys are categorized according to the International Alloy Designation System, with each alloy receiving a four-digit number with the first digit signifying the primary alloying element. Elements such as copper, manganese, silicon, magnesium, magnesium silicon combinations, zinc, and lithium define the individual wrought aluminum alloy categories.

Nickel Alloys

Nickel is a highly compatible material, and as a result can alloy with an array of other metals and materials to create corrosion-resistant or heat-resistant alloys. Nickel-chromium alloys, for example, contain more than 15 percent chromium and are typically used to provide oxidation resistance, especially in applications where temperatures reach 760 degrees Celsius (C) or higher. When considering nickel alloys, it’s helpful to divide them into categories based on the characteristics they offer.

Electrical Resistance Alloys

There are several nickel alloys, called resistance alloys, which are used to help regulate electrical traits. Such alloys include copper-nickel, nickel-chromium-aluminum, nickel-chromium-iron, and nickel-chromium-silicon. All of these alloys have relatively high nickel concentrations.

Resistance Heating Alloys

Heating alloys are typically used in furnaces and related applications to help control heat. Examples of heating alloys include nickel-chromium alloys with 65 to 80 percent nickel and 1 to 2 percent silicon, as well as nickel-chromium-iron alloys with 35 to 75 percent nickel, 1 to 2 percent silicon and 1 percent niobium.

Iron-nickel-chromium and nickel-chromium alloys are typically used because of their strength and heat resistance, making them useful in commercial and military applications. Nickel-copper alloys are frequently used in submarine applications and in other harsh environments because of their high corrosion-resistance.

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