Abstract : ZL～107A casting aluminum alloy is Al~Si～Cu casting high strength aluminum alloy. After heat treatment in the T5 state, the strength can reach σb=420～470MPa. It is necessary to repair welding when manufacturing large, high-strength and complex key engineering structures. The weld seam also requires strength with the base metal. The composition, structure, properties and welding process of ZL～107A casting alloy were studied because ZL～107A was alloyed by adding multiple trace elements on the basis of ZL～107.
Key words : casting; welding; mechanical properties
With the development of modern engineering structures to large, complex and high-strength, the application of high-quality aluminum alloy castings is increasing. Higher requirements are placed on the overall performance of aluminum alloys. It is concentrated in the requirement of high mechanical properties, but also has excellent casting properties. Al-Si-Cu cast aluminum alloy combines the advantages of good mechanical properties of Al-Cu alloy and good casting performance of Al-Si cast aluminum alloy, so it has been the research focus of casting high strength aluminum alloy. BAE354 in the United States and B124 in the former Soviet Union are all Al-Si-Cu high-strength cast aluminum alloys with excellent mechanical properties and good casting properties. China's ZL-107 is also an alloy of this series. ZL-107 contains a high amount of Cu, so the properties of the alloy have potential to be dug. By adding Mg, Zn, Cu, Ti and other trace elements to comprehensively strengthen the alloy, a high strength aluminum alloy ZL-107A is obtained. The properties of the alloy are from σb=280～320MPa, σ0.2=210～230MPa. , δs=3%～4% respectively increased to σb=420～470MPa, σ0.2=325～390MPa, δs=4%～6%, so that the alloy can be applied in the production of modern large-scale and complex aluminum alloy castings. . However, the weldability of this alloy requires inspection by a welding process.
1 alloy composition
The composition of the alloy is shown in Table 1.
Table 1 Chemical composition of ZL～107A
Alloy element content /% impurity content /%
Si 6.5～7.4 Fe(s) ≤0.12
Cu 3.5 to 4.5
Zn 0.8~1.2 Fe(J) ≤0.2
Mg 0.1～0.2
Cd 0.1～0.2
Ti 0.1～0.2 Others ≤0.05
B 0.01~0.05
Be 0.04~0.1 sum 0.3(s)
Al remaining 0.4(s)
l), Si, Mg2Si, AlCu, W (AlxMg5Si4Cu4), TiAl3, AlB2, TiB, according to the phase diagram ZL107A under equilibrium solidification conditions, the phase composition is α (Al) + Si + Al2Cu + W (AlxMg5Si4Cu4), in the casting large When casting, the local crystallization is slow. When the metallographic phase is observed, the microstructure is α(Al)+(α+Si)+Al2Cu, and Al2Cu is distributed on the grain boundary.
3 alloy mechanical properties
The mechanical properties of the alloy are shown in Table 2.
Table 2 Mechanical properties of ZL107A
Casting method state σb/MPa σ0.2/MPa δs/% HBS
Sand type F 175 1~2
Sand type T5 360～380 2～3 125
Metal type F 200 1.5
Metal type T4 370 8～10
Metal type T5 420～470 325～390 4～6 145
As can be seen from Table 2, the alloy has a high overall mechanical properties. In particular, ZL107A has a high yield strength and is close to σb, making it particularly suitable for the manufacture of large and complex key cast aluminum parts in engineering structures.
4 alloy welding process
When there is a defect in the cast structure, it must be repaired. Generally, the welding wire used for the welding of cast aluminum parts is 331, 321 and 311.311, which are aluminum-silicon welding wire, the tensile strength σb is 118 MPa, 321 is aluminum-manganese welding wire, and the tensile strength σb is 118 MPa. According to Table 2, the σb of ZL107A is about 420. ~ 470 MPa, so the mechanical properties of these kinds of welding wire and base metal are quite different. The technical requirement of the casting is that the weld should be consistent with the strength of the base metal, so the commercially available welding wire cannot be used.
If the same material is used to cast the welding wire for the base metal, and the weld structure can be guaranteed to achieve the expected mechanical properties, the welding process should be carefully considered.
First, the same material test piece is cast into a welding wire, and the as-cast test piece is tested and tested to test the weld performance.
Secondly, it is not preheated when welding. Use a larger current to speed up the welding. The welding result is due to the faster melting speed of the weld at high current, and is affected by the larger current during solidification, which is prone to coarse grain structure and low tensile strength. At the same time, the weld structure is prone to cracks under high current. This phenomenon has been confirmed in post-weld metallographic observation and performance tests. Therefore, this process should not be used.
Preheat the test piece to 200-250 °C, use a small current to fill the wire droplet when the surface of the weld is just appearing bright, and the weld will be forwarded when the weld just wets the weld. mobile. The result of this welding is that the molten pool solidifies quickly. Finer grain size is beneficial to improve the mechanical properties of the weld. This welding process uses a current of about 180A.
From the composition of the base material, the Al-Si-Cu alloy, Si and Cu have no adverse effect on the weldability. The Mg content is between 0.1% and 0.2%, and its content is small, which also has little effect on the weldability. In general, the welding wire cast from the same material is equivalent to the remelting process of the base metal in the welding metallurgy, so the metallographic structure and chemical composition of the weld can be basically consistent with the base metal, and the aging treatment with the base metal When the weld is consistent with the mechanical properties of the base metal.
The mechanical properties of the weld were tested after welding, and the test bars were broken at the base material before heat treatment. This is due to the cast structure of the base metal, the grain is coarse before heat treatment, and the weld is stronger than the base material because of the faster cooling rate and finer grain. This has been confirmed in metallographic observations. After the weld is heat treated together with the base metal, the weld fracture zone and the base metal tend to be consistent when observed in the metallographic phase, and cannot be distinguished. This shows that the weld metal composition is basically consistent with the base metal during the welding process, and the argon gas protection effect is still very good. The welding process is basically a remelting process. When the weld is tested with the base material after heat treatment, 3 of the 5 test bars are broken in the base metal, 2 are fractured in the weld, and the tensile strength σb is greater than 400 MPa, while the σb of the cast component body is only up to 372 MPa. , indicating that the welding is successful.
5 Conclusion
ZL107A is an alloy developed by adding multiple trace elements on the basis of ZL107. This alloy has a high comprehensive index of mechanical properties. Through the test, using the appropriate welding process, the weldability of this alloy is still good, the mechanical properties of the weld can reach the standard of the base metal.
About the author : An Zhenzhi (1944-), male, Yantai, Shandong, engineer of Shenyang University of Technology.
Author: An Zhenzhi (School of Materials Science and Engineering, Shenyang University of Technology, Shenyang 110023, China)
Xi Xichuan (School of Materials Science and Engineering, Shenyang University of Technology, Shenyang 110023, China)
Shu-fang WANG (School of Mechanical Engineering, Shenyang University of Technology, Shenyang 110023, China)
references:
[1] Lin Yiqi. Nonferrous Metal Materials Science [M]. Shenyang: Northeast Institute of Technology Press, 1986.
[2] There is a win. Metal welding defects and their prevention [M]. Harbin: Heilongjiang Science and Technology Press, 1995.
[3] American Institute of Metals. Metal Handbook [M]. Beijing: Mechanical Industry Press, 1994
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