Compared with metal fasteners, talk about the advantages of aluminum alloy fastener manufacturing

The weight of aluminum fasteners is 1/3 of the weight of similar steel fasteners. The strength characteristics of this frequently used alloy are surprisingly good. In fact, in terms of strength-to-quality ratio, aluminum fasteners are higher than any other fasteners made of industrial and trade materials. Aluminum is not magnetizable. The thermal and electrical conductivity of aluminum is very good, about 2/3 of the conductivity of copper under the same volume. Aluminum has good processing characteristics and is easy to cold form and hot forge.

Comparison of the strength characteristics of aluminum alloy fasteners and metal fasteners:

The strength characteristics of external thread fastener aluminum alloy materials 2024-T4, 6061-T6 and 7075-T73 are specifically discussed in ASTMF468 on page B-158; nut aluminum alloy materials 2024-T4, 6061-T6 and 6062 The strength characteristics of T9 are discussed in detail in ASTMF467 on page B-184.

It is necessary to explain the two differences in mechanical properties between aluminum alloy threaded fasteners and other metal material fasteners.

The first point is: when calculating the load capacity of a part, the area of u200bu200bthe bottom part of the cross-section is measured instead of the area of u200bu200blarger tensile stress. Only the tensile and yield strength values u200bu200bof the mechanical test specimens given in Table 2 of ASTMF468 are the true strength values. When calculating the strength of the entire size of the fastener, appropriate adjustments can be made. In this way, when multiplying the stress value and the area of u200bu200bthe threaded area by the load capacity in pounds, the calculation result is approximately the product of the true value in the table and the area of u200bu200bthe smaller tooth bottom area.

The second point is that the hardness difference of aluminum alloy is very small, and it is as meaningless as inspection criteria. As an alternative to hardness testing, shear strength testing is usually introduced.

2024-T4 aluminum alloy (containing 4.5% copper, 1.6% manganese, 1.5% magnesium, and the rest is aluminum) is a heavy-duty alloy. It achieves a perfect balance in the combination of strength, corrosion resistance, manufacturability and economy, and is widely used in the manufacture of threaded fasteners.

Bolts, screws and studs made of 7075-T73 aluminum alloy (contains 1.6% copper, 2.5% manganese, 0.3% chromium, and the rest is aluminum) have made slight improvements in strength. And because of the special heat treatment process of T73, it can prevent the occurrence of stress corrosion to a large extent. But the high cost has restricted its popularity.

6061-T6 aluminum alloy (containing 0.6% silicon, 0.25% copper, 1% magnesium, 0.2% chromium, and the rest is aluminum) can be used to design internal and external threads with higher requirements for corrosion resistance fastener.

6062-T9 aluminum alloy (containing 0.6% silicon, 0.25% copper, 1% magnesium, 0.09% chromium, 0.5% lead, and the rest is aluminum) is almost exclusively for design nuts. This alloy is stronger than 6061-T6 aluminum alloy and has relatively better corrosion resistance.

The full-thickness nut made of 6062-T9 aluminum alloy has enough strength to match the bolts made of 2024-T4 or 7075-T73 aluminum alloy. Machine screws, nuts and other 1/4 inch and smaller nuts are made of 2024-T4 aluminum alloy.

Advantages of aluminum alloy used in fastener manufacturing

The four aluminum alloys mentioned are the most widely used in the manufacture of threaded load-bearing fasteners, while other aluminum alloys are used in the manufacturing of other types of fasteners. The small solid, half pipe and blind rivets are made of 1100-F, 5052-F, and 5056-F aluminum alloys. The heat-treatable 2017-T4, 2117-T4, 2024-T4, 6061-T6 aluminum alloy and the relatively newly developed 7075-T73 aluminum alloy have superior shear strength and can drive without pre-transmission treatment. .

Flat washers are usually made of aluminum-plated 2024-T4 alloy; spiral spring washers are usually made of 7075-T6 alloy; tapping screws can be made of 7075-T6 alloy; self-tapping screws are made of the same material alloy through anode Handle it. The 2011-T3 aluminum alloy (containing 5.5% copper, 0.5% lead, 0.5% bismuth, and the rest is aluminum) can be used to make parts for thread cutting machines.

Under normal circumstances, aluminum has sufficient corrosion resistance. And when the expected exposure environment is very harsh, its corrosion resistance can be greatly improved by anodizing. Anodizing is an electrical machining process that forms an oxide film on the metal surface. Anodizing not only enhances the ability to resist corrosion, but also enhances the ability to protect against wear and scratches. The anode coating comes in many colors for decoration and identification purposes. In atmospheric corrosion, aluminum forms a light gray oxide film on the surface. These corrosion products will not contaminate the surface of aluminum, or spread to the adjacent surface, which is different from the performance of many other metals under the effect of corrosion.

The tensile strength of pure aluminum is about 13,000 psi. It is possible to increase the strength greatly by adding a small amount of alloying elements. Aluminum alloys of 2XXX, 6XXX, and 7XXX have a good effect on heat treatment. Therefore, virtually all threaded fasteners used for load transfer are made of these three major types of aluminum alloys. There are four aluminum alloys that are almost dedicated.