All About 6061 Aluminum Alloy

An aluminum alloy is a blend of aluminum, as the main element, with other known elements. Aluminum alloys typically consist of aluminum and elements such as: magnesium, tin, chromium, copper, silicon, and manganese. These alloying elements are not necessarily combined in this order—and, it is not mandatory that all the elements should be present. Depending on the application, the specific alloying elements may be chosen and properly combined in quantifiable measures to form aluminum alloys. However, these metallic elements are combined with aluminum to the end that the new material formed will have improved strength, mechanical properties, durability, corrosion resistance, workability, etc. These metallic elements together with aluminum are mixed in their molten form to form a substance or material that is homogeneous after cooling takes place. Aside from the improved qualities, aluminum alloys are known to be cost-effective compared to pure aluminum because of its lower melting point. A lower melting point implies that lower heat energy will be consumed during subsequent manufacturing processes.

The alloy composition of 6061 aluminum is aluminum (97.9 %), magnesium (1.0 %), silicon (0.6 %), copper (0.28 %), chromium (0.2 %), and a trace amount of other elements. A variety of aluminum alloys are available. Each of them is specified by a code number, such as the 6000 series, 7000 series, and 1000 series. Moreover, each digit of the number is representative of certain attributes that uniquely identify the aluminum alloys. In the case of 6061 aluminum, which is part of the 6000 series, the  initial number 6 indicates that the primary alloying elements are magnesium and silicon. These elements are present in greater quantities than the other alloying elements. 

The second digit emphasizes impurity control and that due attention should be given as the alloying elements are combined with the base aluminum element. Therefore, the number 0 in 6061 indicates that no special care is required to tighten controls. The third and fourth digits only identify the alloys within their series, without any particular meaning. However, this is not the case with the 1000 series, in which the last two digits represent the minimum additional purity above 99 %. For example, 1000 and 1050 indicate that the alloy would have 99 % and 99.5 % minimum aluminum, respectively. 

Some of the characteristics of 6061 aluminum include: good weldability, machinability, corrosion resistance, and workability. Generally, the corrosion resistance and strength are improved through tempering. Tempering is the process of enhancing the characteristics of metal by subjecting it to a high temperature. The alloy is heated to a temperature just below the melting point. Tempering strengthens the alloy by reducing its brittleness and internal stresses.

Table 1 below highlights some material properties of 6061 aluminum. The material properties include but are not limited to, the mechanical properties, processing properties, and thermal properties:

6061 aluminum strength depends on the tempered grade, including 6061-O, 6061-T4, and 6061-T6. With 6061-T6, for example, the parameters for measuring how strong it is depends on the yield and tensile strengths. The yield strength of a material measures its allowable stress limit when force is applied to it. When the force exerted is above this value, permanent deformation will take place and the material is unable to return to its original shape. On the other hand, the tensile stress of a material is the maximum stress above which it will fail and break. That said, the yield stress of 6061-T6 aluminum is at least 35,000 psi or 241 Mpa. While its tensile stress is a value upwards of 42000 psi or 290 Mpa.

The things to consider when choosing an aluminum grade are listed below:

1. Corrosion resistance
2. Weldability
3. Workability
4. Strength
5. End-use application
6. Heat treatment
7. Machinability

Aluminum alloys come in a variety of shapes and grades. The selected aluminum grade depends to a large extent on the end-use application. When the end-use is defined, it will be easier to rank the attributes or characteristics of each grade. The grade that matches the desired attribute can be chosen. For example, if a project requires an alloy that has good weldability without putting so much emphasis on strength, alloy 1100 is a good option. The reason is that it has good weldability but is not suited to high-strength applications. 

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