Method for reducing welding porosity through pre-welding air heat treatment of additive manufacturing aluminum-silicon alloy

Abstract

The invention discloses a method for reducing welding porosity through air heat treatment before additive manufacturing aluminum-silicon alloy welding, and relates to the field of additive manufacturing metal material post-treatment. The method comprises the following steps: heating an aluminum alloy sample subjected to additive manufacturing in a tubular furnace to 140-280 DEG C, preserving heat in the furnace for 2-72 hours, and cooling in air to room temperature. Before welding, the surface of the sample subjected to heat treatment is subjected to alkali washing and acid washing chemical cleaning. According to the method, through air heat treatment with the optimized heating temperature and heat preservation time, the porosity of an Al-Si alloy weld joint manufactured through the additive can be effectively reduced, and therefore the mechanical property of a joint is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of additive manufacturing aluminum alloy material treatment, and specifically to a method for reducing welding porosity by pre-welding air heat treatment of additive manufacturing aluminum alloy. Background Art

[0002] Al-Si alloys have great application potential in the aerospace field due to their good printability and excellent strength-to-weight ratio. In addition, different from the combination forming of multiple individual components in traditional manufacturing methods, additive manufacturing technology can directly form complex structures at one time, significantly improving production efficiency, reducing manufacturing costs, and shortening the production cycle.

[0003] However, due to the limitation of the forming chamber size, it is difficult to meet the one-time direct forming requirements of large-size and complex-shaped parts. Therefore, using appropriate welding technology to connect printed parts to each other or to connect them to traditionally manufactured components is an effective way to break through this limitation. In addition, by welding and repairing damaged printed parts during use, more costs and time can be saved compared to replacing new parts. Therefore, the welding of printed parts is of great significance.

[0004] However, it is very difficult to obtain high-quality fusion welded joints of additive manufacturing aluminum alloys. This is because during the laser printing process, the hydrogen content in additive manufacturing aluminum alloys is relatively high. When welding, hydrogen escapes, forming a large number of hydrogen pores, resulting in the welds of additive manufacturing aluminum alloy fusion welded joints being extremely prone to hydrogen pores.

[0005] In traditional aluminum alloys, heat treatment is a commonly used method for removing hydrogen from aluminum alloys. Therefore, heat treating additive manufacturing Al-Si alloys is a low-cost and simple-to-operate method for reducing welding porosity, and it can be applied to the actual production process. However, research shows that if the heat treatment temperature is too high, it will cause the Si network to break, thereby leading to a decline in the mechanical properties of aluminum alloys. Currently, there are studies on pre-welding solution heat treatment and pre-welding vacuum heat treatment to reduce weld porosity. However, when the temperature is around 500°C, it has a greater impact on the decline of material mechanical properties. How to optimize the process to reduce porosity while basically not losing mechanical properties is an urgent problem to be solved. Therefore, the present invention creatively selects a temperature range lower than the traditional heat treatment temperature range, and the temperature range is 140°C to 280°C. Summary of the Invention

[0006] The implementation of the present invention provides a method for reducing welding porosity by pre-welding air heat treatment of additive manufacturing aluminum-silicon alloys. By performing pre-welding low-temperature heat treatment on additive manufacturing aluminum alloy specimens at different temperatures and times, while removing the stress generated during the printing process, the hydrogen content in the printed specimens is reduced, thereby reducing porosity and making the additive manufacturing aluminum-silicon alloy specimens meet the aerospace use requirements.

[0007] To solve the above technical problems, the embodiments of the present application disclose the following technical solutions: A method for reducing the welding porosity of an additively manufactured aluminum-silicon alloy by pre-welding air heat treatment. The heat treatment method includes the following steps: subjecting the prepared additively manufactured Al-Si alloy specimen to air heat treatment before welding, and cleaning the surface before welding after heat treatment. The method of pre-welding air heat treatment is: heating the base metal specimen in a heat treatment furnace to 140°C to 280°C, keeping it in the furnace for a holding time of 2 to 72 hours, and then taking out the specimen and cooling it in air to room temperature.

[0008] Specifically: Set the program to the predetermined heat treatment temperature and holding time; wait for the furnace temperature to rise to the predetermined heat treatment temperature of 140 to 280°C, place the specimen in the furnace, start the heat treatment process, with a holding time of 2 to 72 hours, and after the holding ends, take out the specimen and cool it naturally in air.

[0009] The additively manufactured Al-Si alloy specimens include AlSi10Mg, AlSi12, and AlSi7Mg alloys, and the additive manufacturing methods include powder bed laser melting forming, laser directed energy deposition, and arc wire additive manufacturing.

[0010] The aluminum-silicon alloy is preferably AlSi10Mg alloy; the surface of the AlSi10Mg alloy specimen is mechanically polished before welding after heat treatment, chemically cleaned after mechanical polishing, and then all specimens are alcohol-cleaned. The L-PBF formed parts are mechanically polished with sandpaper, and mechanically polished successively with 50, 600, and 800 mesh sandpapers; the chemical cleaning is carried out with a 6 to 8% (w%) sodium hydroxide solution at 50°C for 9 to 10 minutes, and then with a 45 to 50% (v%) nitric acid solution at room temperature for 7 to 8 minutes.

[0011] After heat treatment, welding is carried out, and the welding method is fusion welding.

[0012] After pre-welding heat treatment and pre-welding surface cleaning, the parameters that the additively manufactured AlSi10Mg alloy welded joint can achieve are as follows:

[0013] The hardness is maintained at: 90.1Hv to 97.5Hv, and the porosity is reduced to: within the range of 2.27% to 9.47%. Description of the Drawings

[0014] Figure 1 For the cross-sectional morphology of the joint after TIG welding at a pre-welding heat treatment temperature of 140°C (a) without heat treatment; (b) 30h; (c) 72h.

[0015] Figure 2 For the longitudinal-sectional morphology of the joint after TIG welding at a pre-welding heat treatment temperature of 140°C (a) without heat treatment; (b) 30h; (c) 72h.

[0016] Figure 3 Cross-sectional morphologies of the joints after TIG welding at the pre-welding heat treatment temperature of 280 °C: (a) without heat treatment; (b) 10 h; (c) 20 h.

[0017] Figure 4 Longitudinal-sectional morphologies of the joints after TIG welding at the pre-welding heat treatment temperature of 280 °C: (a) without heat treatment; (b) 10 h; (c) 20 h.

[0018] Figure 5 Contents of H and O in the base metal under different heat treatment temperatures. Specific embodiments

[0019] The following non-limiting embodiments can enable those of ordinary skill in the art to fully understand the present invention, but do not limit the present invention in any way.

[0020] In the following embodiments, the test methods are conventional methods unless otherwise specified; the reagents and materials can be obtained from commercial sources unless otherwise specified.

[0021] Example 1

[0022] This example provides a method for reducing the welding porosity of additively manufactured aluminum alloys by pre-welding air heat treatment.

[0023] The heat treatment steps are as follows: gradually raise the temperature in the heat treatment furnace to 140 °C at a heating rate of 5 °C / min, hold for 72 h, and then take it out for air cooling after the holding time ends;

[0024] Mechanically polish the surface of the heat-treated AlSi10Mg alloy specimens, chemically clean them after mechanical polishing, and then wash all specimens with alcohol. Mechanically polish the L-PBF formed parts with sandpaper, and mechanically polish them successively with 50, 600, and 800-mesh sandpapers; the chemical cleaning is carried out with a 6-8% (w%) sodium hydroxide solution at 50 °C for 9-10 min, and then with a 45-50% (v%) nitric acid solution at room temperature for 7-8 min.

[0025] Weld the specimens together in a butt joint manner. The welding method used is TIG welding. After parameter optimization, the welding parameters are selected as follows: current: 95 A, welding speed: 5 mm / s, welding voltage: 20 V. The hardness is 97.5 Hv when the holding time is 30 h, and the hardness is 95.2 Hv when the holding time is 72 h.

[0026] After welding, the specimens were cut by wire cutting and metallographic specimens of the cross-section and longitudinal section were prepared. The specimens were cold-mounted metallographically, then the surfaces of the specimens were mechanically polished, and then the surfaces of the specimens were etched with Keller's reagent and then metallographic observation was carried out to show the cross-sectional and longitudinal-sectional morphologies of the joints. The porosity of the cross-section and longitudinal section of the joints in Example 1 was measured as shown in Table 1 and Table 2. It can be seen from Table 2 that when the heat treatment temperature was 140 °C and the holding time was 72 h, the porosity was 6.87%. Compared with the non-heat-treated porosity, it decreased by 3.91%. From Figure 5 It can be seen that the reduction of hydrogen pores is due to the decrease of hydrogen and oxygen contents in the base metal. It can be seen from Table 5 that the hardness of the non-heat-treated weld is 103.1 Hv, and the hardness of the weld heat-treated at 140 °C / 72 h is 95.2 Hv, and the hardness decreased slightly.

[0027] Example 2

[0028] This example provides a method for reducing welding porosity by pre-welding air heat treatment of additive manufacturing aluminum alloy.

[0029] The heat treatment steps are as follows: gradually raise the temperature in the heat treatment furnace to 280 °C at a heating rate of 5 °C / min, hold for 20 h, and take it out for air cooling after the holding time ends;

[0030] The surfaces of the heat-treated AlSi10Mg alloy specimens were mechanically polished, chemically cleaned after mechanical polishing, and then all specimens were cleaned with alcohol. The L-PBF formed parts were mechanically polished with sandpaper, and mechanically polished with 50, 600, and 800-mesh sandpapers in sequence; chemical cleaning was carried out with a 6-8% (w%) sodium hydroxide solution at 50 °C for 9-10 min, and then with a 45-50% (v%) nitric acid solution at room temperature for 7-8 min.

[0031] The specimens were welded together in a butt joint manner, and the welding method used was TIG welding. After parameter optimization, the welding parameters were selected as follows: current: 95 A, welding speed: 5 mm / s, welding voltage: 20 V. The hardness was 97.5 Hv when the holding time was 30 h, and the hardness was 95.2 Hv when the holding time was 72 h.

[0032] After welding, the specimens were cut by wire cutting and metallographic specimens of the cross-section and longitudinal section were prepared. The specimens were cold-mounted metallographically, then the surfaces of the specimens were mechanically polished, and then the surfaces of the specimens were etched with Keller's reagent and then metallographic observation was carried out to show the cross-sectional and longitudinal-sectional morphologies of the joints. The porosity of the cross-section and longitudinal section of the joints in Example 2 was measured as shown in Table 3 and Table 4. It can be seen from Table 3 that when the heat treatment temperature was 280 °C and the holding time was 10 h, the porosity was 4.1%. Compared with the non-heat-treated porosity, it decreased by 6.29%. Figure 5It can be seen that the reduction of hydrogen pores is due to the decrease in the hydrogen and oxygen content in the base metal. As shown in Table 5, the hardness of the non-heat-treated weld is 103.1 Hv, and the hardness of the weld heat-treated at 280 °C for 20 h is 90.1 Hv, showing a slight decrease in hardness.

[0034] Table 1 Statistics of the porosity of the joint cross-section at different times at 140 °C

[0035]

[0037] Table 2 Statistics of the porosity of the joint longitudinal section at different times at 140 °C

[0038]

[0040] Table 3 Statistics of the porosity of the joint cross-section at different times at 280 °C

[0041]

[0043] Table 4 Statistics of the porosity of the joint longitudinal section at different times at 280 °C

[0044]

[0046] Table 5 Cross-sectional hardness of the joint at different times and temperatures

[0047]

Claims

1. A method for reducing welding porosity by air heat treatment before welding of aluminum-silicon alloy in additive manufacturing, characterized in that: The prepared additively manufactured Al-Si alloy specimens were subjected to air heat treatment before welding, and the surface was cleaned after heat treatment and before welding. The method of air heat treatment before welding is: the base material specimen is heated to 140℃~280℃ in a heat treatment furnace, and the holding time in the furnace is 2~72h, and then the specimen is taken out and placed in the air to cool to room temperature.

2. The method according to claim 1, characterized in that The aluminum alloy samples were mechanically polished and chemically cleaned on the surface after heat treatment and before welding. The aluminum alloy samples were mechanically polished with sandpaper; the chemical cleaning was carried out by using a 6-8% (w%) sodium hydroxide solution at 50°C for 9-10 minutes, and then using a 45-50% (v%) nitric acid solution at room temperature for 7-8 minutes.

3. The method according to claim 1, characterized in that: The additively manufactured Al-Si alloy specimens include AlSi10Mg, AlSi12 and AlSi7Mg alloys, and the additive manufacturing methods include powder bed laser melting, laser directed energy deposition and arc fuse additive manufacturing.

4. The method according to claim 1, 2 or 3, characterized in that: Fusion welding methods include TIG, MIG, CMT, laser and electron beam welding.

5. The method according to claim 1, characterized in that The hardness is maintained at 90.1Hv to 97.5Hv, and the porosity is reduced to within the range of 2.27% to 9.47%.

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