Low-volume thin-walled containers, part rough cast is mostly ZL115 pressure. Although the X-ray flaw detection after casting, but due to limitations and structural characteristics of the size and distribution of casting defect sensitive direction, some of the defects in the X-ray films can not clearly presented, often found after mechanical processing, and some small diameter through of pore pressure test only after the discovery. This seriously affects the quality of products and production schedules, or even result in huge economic losses. Some conventional welding methods can not satisfy the technical requirements. To verify that the new process to solve the aluminum parts machined sealing occurs after the appearance of bug fixes and the effectiveness of an aluminum casting to find out new ways to repair defects, we conducted a large number of tests and the necessary testing process, and the formation of a correct process aluminum casting defect repair procedures.
2, the metal surface defect repair machine repair mechanism
Because the chemical and lively aluminum and its alloys are highly vulnerable to the formation of surface oxide film, and many are refractory nature (such as the melting point of Al2O3 is about 2050 ℃, MgO melting point of about 2500 ℃) thermal conductivity of aluminum and its alloys in addition strong, fusion welding is not likely to cause the phenomenon. The same proportion of aluminum oxide film as the proportion of extremely close, so it is easy to become a weld metal inclusions. Aluminum and its alloys also coefficient of linear expansion, thermal conductivity and strong, prone to warping during welding. This is quite welding aluminum and its alloys difficult problem. Currently the most commonly used fusion welding arc is by "cathode spray" effect, breaking the oxide film, under the protection of argon gas, the oxide film can not be regenerated. But in the welding of aluminum alloy after heat treatment enhanced when there is strength near the weld area greatly reduced the phenomenon, inevitably will produce warpage. Metal surface repair machine is mainly used to repair the casting defects, it has high + pulse power inverter, allows high-speed rotating wire torch and control components. The mechanism of its repair defect: high frequency pulse voltage + the formation of the gas breakdown plasma gas, resulting in temperatures up to above 6000 ℃ EDM, EDM will fusible rotating electrode (the wire) instant (10-5 -10-6 sec) and in contact with the base material while melting and rely on instantaneous high temperature and rotation welding wire and base metal and rotating mechanical friction polishing the combined effects of electrostatic force, so that oxide film broken, under the protection of argon gas, the oxidation film can not be re-generated, thus completing the welding wire and base metal metallurgical bonding. Short duration of action as EDM, wire in direct contact with the base metal partial melting, good thermal conductivity of aluminum, the moment will spread and dissipate the heat input into the air, almost no temperature rise matrix, which matrix is ??not deformed, precision aluminum casting machining defects after repair, but will not affect the dimensional accuracy. Repair file repair the surface after grinding or machining, the appearance of the matrix can be consistent.
3, the patch test materials:
ZL115 heat treatment: quenching and artificial aging is not entirely Wire: S311 standard form of Al-Si wire sample: test plate slot, after opening with a cast aluminum machine repair defect repair after the Preparation of metallographic specimens.
4, microstructure and analysis
Enhanced by heat treatment with aluminium welding wire, the welding heat affected zone can be broadly divided into the following organizational areas: 1) semi-melted zone (the area prone to over-burning); 2) non-uniform solid solution area (solid partial decomposition of the melt area of ??coarse grains); 3) annealed to soften area (area over time). Alloy in semi-molten zone conditions on the performance of welded joints most affected. Basically, the strength of welded structures depends on the organization of half-melted zone change. If you produced a half-melted zone burning phenomenon, not only more to promote the formation of hot cracks in this area, but also greatly reduce the joint strength and ductility. Heat strengthened aluminum joints under static tensile test, often semi-melted zone along the fracture. Alloy in semi-molten zone is not greater than the intensity before the strength of the alloy solder 50-70 ℅. Melted zone in the semi-solid melt zone after the non-uniform, characterized by: alloying elements in grain production around the uneven concentration of relatively coarse grains. After solid-melt zone in the uneven softening annealing zone, prone to coarse grains and the thickness of a large network of second phase inclusions. Metal surface repair machine defects during the repair of aluminum and its alloys, due to increase in welding wire and base metal is the instantaneous pulse current between the instantaneous generation ultra-high temperature, so that the instantaneous welding wire and base metal melting crystalline moment, it does not exist a continuous melting pool, almost no base metal temperature, thus there is no heat affected zone. It's near the weld area there is only a half-melted zone. Obviously, in the semi-molten region does not produce over-burning phenomenon, the microstructure of the base metal did not change significantly.
5, the actual piece casting defect repair:
A ф540, wall thickness 6 mm cast aluminum housing for 0.3MPa in the leak tightness test found. Deep in the defect site ф6mm 3mm drill hole, for bug fixes. Welding parameters: frequency of 600HZ, 45% duty cycle, output amplitude 41%, 79% speed, the shell has 0.3MPa for 10 gas-tight and 0.9 MPa external pressure strength test showed no leakage.
6, results and analysis
The results showed that when the new technology in the patch formation does not like the welding pool, which is rotated by the electric spark to the wire aluminum electrode, while contact with the base metal and wire forming part of the molten metal produced localized melting metallurgical bonding. Weld is a very small dendritic cast structure, the matrix is ??also a cast structure, the difference is that crystal orientation is different. Does not exist on the base metal heat affected zone of reduced strength. Generated by the base metal temperature is extremely small, semi-molten zone not been burning phenomena, a fine grain size, there appeared in the argon arc welding fusion zone and the uneven soft annealed solid areas, will not heat cracks and strength, plastic the phenomenon of decline, as there is no such pool welding process, molten metal melting moment, instant crystallization time is very short (μms level), despite the instantaneous temperature, it will not cause the accuracy of the base metal make-inch change, but As a piece of deposited metal is melted, a piece of crystal solidification, whether the compact between the film and film combination and the operator's job skills to some extent.
Based on the above results and analysis, and we used to do tensile and hardness results of the experimental data to prove that parts in the welding process, non-heating, deformation, reduced level of small matrix strength, to meet the national standard, compact metal welding point No burn marks, fill material consistent with macro-base material. We believe that using this method of welding aluminum defect repair is feasible, we have every reason to this repair method is defined as a new welding method, this new welding method, an extremely broad application prospects.
First, the preparation of welding instructions welding instructions welding process is the basis for assessment and evaluation of the original object, the welding process should be assessing the content of all reflected. Include: the natural conditions of welded joints, base material type, welding method, welding material, welding current, welding voltage, welding speed, preheat temperature. Welding instruction is usually recommended in the standard format, you can also design their own format.
Second, the provisions of the standard welding conditions for specimen preparation; by the unit of skilled welding personnel using welding electrode welding of the unit sample; used in welding conditions should strictly abide by the welding process instructions;
Third, the physical and chemical experimental pilot projects identified in accordance with the relevant standards; preparation of various properties in accordance with the standard sample; in accordance with the standards of a variety of performance tests; fill in test reports of each pilot project.
Fourth, the preparation of welding procedure qualification welding consumable qualification report on the welding procedure qualification report is a comprehensive summary of tests, so the test results should be summarized, and gives the final conclusion. Welding procedure qualification reports of the role: as a basis for development of welding procedures, with guidance. Welding procedure qualification report is usually recommended in a standard format.