Method for remelting and regulating solidification phase morphology in Al-Si hypoeutectic casting alloy

Abstract

The present application belongs to the technical field of aluminum alloy material processing, and discloses a method for remelting and controlling the solidification phase morphology in Al-Si hypoeutectic casting alloy, which comprises the following steps: after completely melting the raw materials for preparing the Al-Si hypoeutectic casting alloy, heat preservation is carried out at T1, T1>(T lid +50℃);after cooling to T2, heat preservation is carried out, T2≤T sol ; after heating to T3, heat preservation is carried out for t min, T3=T4‑m×(100‑C), t=(T4‑T3) / 6m; casting, cooling, and obtaining the alloy material B, so that the solidification phase morphology in the casting aluminum alloy can be controlled. The method can effectively control the solidification structure through the melting process of the casting aluminum alloy, and is easy to realize industrial production.

Description

Technical Field

[0001] This invention relates to the field of aluminum alloy material processing technology, and in particular to a method for controlling the morphology of solidified precipitates in Al-Si hypoeutectic cast alloys through remelting. Background Technology

[0002] Cast aluminum alloys are a very important type of engineering material due to their advantages such as low density, high specific strength, high corrosion resistance, and good dimensional stability. They are widely used in gas turbine blades, pump bodies, brackets, wheel hubs, intake lips, and engine casings, as well as in the manufacture of cylinder heads, gearboxes, pistons, instrument housings, and turbocharger pump bodies for automobiles.

[0003] However, due to the wide crystallization temperature range and significant solidification shrinkage of cast aluminum alloys, the primary aluminum-rich phase and eutectic silicon phase tend to have coarse morphologies, resulting in severe macroscopic segregation in the casting structure. This easily leads to casting defects such as pinholes, porosity, and inclusions, severely reducing the quality of the casting. To address these issues in cast aluminum alloy castings and their solidification structures, it is generally necessary to add grain refiners or modifiers during the solidification process, or apply pressure fields or multi-field coupling methods such as ultrasonic and vibration fields to refine the solidification structure, break up or release the primary aluminum-rich phase, and reduce casting defects such as pinholes, porosity, and inclusions, thereby improving the forming quality of the cast aluminum alloy castings.

[0004] To further simplify and improve the forming quality of cast aluminum alloy parts, existing technology proposes a vacuum laser remelting surface modification method. This method involves completely melting the alloy surface with a laser, followed by rapid solidification, forming a fine-grained structure on the surface layer to achieve surface modification. The reason for the formation of a fine-grained structure after complete remelting of the surface metal in this laser surface remelting method is that the solidification of the remelted surface metal occurs under conditions of high thermal conductivity; that is, the latent heat of crystallization released when the thin layer of molten metal solidifies is absorbed by the unmelted metal at the bottom. This remelting method is clearly unsuitable for the solidification process of large-volume cast aluminum alloys because the fully remelted alloy melt will re-nucleate and grow. At this point, the large-volume cast aluminum alloy melt cannot conduct heat as quickly as surface remelting, thus generating new coarse aluminum alloy structures. Existing technology also provides a method for preparing micro / nano-structured bulk silicon materials by combining laser surface remelting with chemical dealloying. This method employs laser-assisted surface remelting of aluminum-silicon casting alloys, followed by cutting off the remelted layer. Finally, an etchant is used to dealloy the remelted layer, removing elemental aluminum and ultimately obtaining micro / nano-structured bulk silicon material. This method can refine the silicon phase in cast aluminum alloys. However, for large-volume cast aluminum alloy melts and their precision castings, methods other than remelting, such as etching, are clearly insufficient for industrial-scale production of cast aluminum alloy castings.

[0005] Therefore, the present invention provides a method for controlling the morphology of solidified precipitates in Al-Si hypoeutectic casting alloys through remelting. Summary of the Invention

[0006] To address the problems of coarse morphology and size of solidified precipitates, severe compositional segregation, and numerous casting defects in the solidification microstructure of cast aluminum alloys, leading to poor alloy mechanical properties, this invention provides a method for controlling the morphology of solidified precipitates in Al-Si hypoeutectic cast alloys through remelting. This method involves partially remelting the solidified precipitates through remelting, achieving dendrite fragmentation, freeing, refinement, and microstructure homogenization of the solidified precipitates. This method effectively refines and optimizes the solidification microstructure of cast aluminum alloys, enabling effective control of the solidification microstructure during the casting process, and is easily implemented in industrial production.

[0007] The method for controlling the morphology of solidified precipitates in Al-Si hypoeutectic cast alloys by remelting according to the present invention is achieved through the following technical solution:

[0008] A method for controlling the morphology of solidified precipitates in Al-Si hypoeutectic cast alloys through remelting includes the following steps:

[0009] Step 1: After completely melting the raw materials for preparing the Al-Si hypoeutectic casting alloy, heat treatment is carried out at temperature T1 to obtain melt A;

[0010] Wherein, T1>(T lid +50℃), T lid This is the liquidus temperature of the alloy;

[0011] Step 2: Cool the melt A to T2 and then hold it at that temperature to obtain alloy material A;

[0012] Where T2≤T sol T sol The solidus temperature of the alloy;

[0013] Step 3: Heat the alloy material A to T3 and hold it at that temperature for t min to achieve remelting of the alloy material A and obtain melt B;

[0014] Where T3 = T4 - m × (100 - C), t = (T4 - T3) / 6m;

[0015] T4 is the melting point of pure aluminum, m is the average slope of the liquidus line for the precipitation of the primary aluminum-rich phase, and C is the percentage content of aluminum in the cast aluminum alloy.

[0016] Step 4: Cast the melt B and cool it to obtain alloy material B, thus realizing the control of the solidification morphology of Al-Si hypoeutectic casting alloy.

[0017] Furthermore, in step 1, the heat preservation time needs to be selected based on the heat preservation temperature T1. This invention takes into account that T1>(T lid (+50℃), therefore the heat treatment time for this step is ≥10min to ensure that each raw material is fully melted and thoroughly heated and mixed.

[0018] Furthermore, the present invention further optimizes the heat preservation time in step 1 to be 10-30 minutes.

[0019] Furthermore, in step 2, the heat preservation treatment involves cooling melt A and then holding it at that temperature. This allows the primary aluminum-rich phase (α-Al) and α-Al plus eutectic silicon to precipitate and grow sequentially during this process. Therefore, T2 in this step is the precipitation temperature. In this embodiment, considering that the heat preservation time in this step is related to the precipitation temperature T2, the heat preservation time is 0.5–3 minutes.

[0020] Furthermore, the present invention further optimizes the heat preservation time in step 2 to be 0.5 to 1.5 min.

[0021] Furthermore, the Al-Si hypoeutectic casting alloy is either Al-12Si casting aluminum alloy or Al-6Si casting aluminum alloy.

[0022] Furthermore, when the Al-Si hypoeutectic cast alloy is an Al-12Si cast aluminum alloy, it is composed of the following atomic mass percentage components:

[0023] 88 wt.% Al and 12 wt.% Si.

[0024] Furthermore, when the Al-Si hypoeutectic cast alloy is an Al-6Si cast aluminum alloy, it is composed of the following atomic mass percentage components:

[0025] 94 wt.% Al and 6 wt.% Si.

[0026] Furthermore, the temperature of the casting process is T3.

[0027] Compared with the prior art, the present invention has the following advantages:

[0028] To address the problem of coarse precipitate morphology in the solidification structure of cast aluminum alloys after conventional melting and casting methods, resulting in poor alloy casting performance, this invention proposes a method to control the morphology and size of solidified precipitates in cast aluminum alloys through remelting. This method is based on interface stability analysis and considers the influence of composition gradient and interfacial energy on the morphology of precipitates. After the solidified phase precipitates, the system temperature is reheated to the gap between its solidus and liquidus temperatures by temperature control. The system is then held at this temperature gap, causing the primary solid phase to become unstable, fragmented, and free under the influence of composition gradient and interfacial energy. This process refines the size of the precipitates and rounds the morphology of the primary phase.

[0029] The method of this invention can effectively refine and optimize the solidification structure of cast aluminum alloys, achieving effective control over the solidification structure during the casting process, and is easy to implement for industrial production. This invention has broad application prospects in high-performance, low-cost, and shape- and property-controlled casting of aluminum alloys. Attached Figure Description

[0030] Figure 1 A flowchart for controlling the morphology of solidification precipitates in the remelting process of cast aluminum alloys;

[0031] Figure 2 Schematic diagram of primary aluminum-rich phase refinement during remelting of cast aluminum alloys;

[0032] Figure 3 The image shows the microstructure of the multi-element alloy material at a scale of 10 mm, as shown in Comparative Example 1.

[0033] Figure 4 The image shows the microstructure of the multi-element alloy material at the 100 μm scale in Comparative Example 1.

[0034] Figure 5 This is a grain size distribution diagram of the alloy material in Comparative Example 1;

[0035] Figure 6 This is a micrograph of the multi-element alloy structure of alloy material B in Example 1 at a scale of 10 mm.

[0036] Figure 7 This is a photograph of the microstructure of alloy material B in Example 1 at the 100 μm scale;

[0037] Figure 8 This is a grain size distribution diagram of alloy material B in Example 1;

[0038] Figure 9 The image shows the microstructure of the multi-element alloy material at a scale of 10 mm for Comparative Example 2.

[0039] Figure 10This is a micrograph of the multi-element alloy structure of alloy material B in Example 2 at a scale of 10 mm. Detailed Implementation

[0040] This invention takes into account the wide crystallization temperature range of cast aluminum alloys, meaning that the solidification of the primary aluminum-rich phase needs to occur within a large temperature range. This provides the possibility of further controlling solute diffusion and interface migration by adjusting the system temperature (within the crystallization temperature range of the primary aluminum-rich phase), thereby further controlling the stability of the primary aluminum-rich phase. By controlling the stability of the primary aluminum-rich phase, the transformation from coarse primary aluminum-rich phase dendrites to equiaxed grains can be achieved, thus refining the alloy microstructure, reducing macroscopic segregation in castings, suppressing the formation of casting defects such as pinholes, porosity, and inclusions, and obtaining cast aluminum alloy castings with significantly improved microstructure and forming quality. The technical solutions in the embodiments of this invention will be clearly and completely described below with reference to the accompanying drawings.

[0041] Example 1

[0042] Please see Figure 1 This embodiment takes Al-12Si cast aluminum alloy (88% aluminum by mass and 12% silicon by mass) as an example to provide a method for controlling the morphology of solidified precipitates in Al-12Si cast aluminum alloy by remelting, including the following steps:

[0043] Step 1: According to the composition percentage of Al-12Si cast aluminum alloy, that is, the ratio of 88wt.% aluminum and 12wt.% silicon, weigh the corresponding mass of aluminum ingots and crystalline silicon raw materials, melt them completely in the melting furnace, and then hold them at temperature T1 to obtain melt A.

[0044] Where, T1>(T lid +50℃), this embodiment takes into account the liquidus temperature T of the primary aluminum-rich phase in the Al-12Si alloy. lid The temperature is approximately 578℃, so T1 is selected as 700℃ in this embodiment. The heat preservation treatment in this step is mainly to ensure that the raw materials are fully heated and mixed. The heat preservation time needs to be selected according to the heat preservation temperature T1. In this embodiment, the heat preservation time is 10 minutes.

[0045] Step 2: Cool the melt A to T2 and then hold it at that temperature to obtain alloy material A;

[0046] Where T2 ≤ the solidus temperature of the alloy, in this embodiment, considering that the liquidus temperature of the primary aluminum-rich phase in the Al-12Si alloy is 578℃, T2 is selected as 565℃. Furthermore, in this step, after cooling melt A, a heat-holding treatment is performed to allow the primary aluminum-rich phase (α-Al) and α-Al plus eutectic silicon to precipitate and grow sequentially during this process. Therefore, T2 in this step is the precipitation temperature. Considering that the heat-holding time in this step is related to the precipitation temperature T2, the preferred heat-holding time is 1 minute.

[0047] Step 3: Heat the alloy material A to T3 and hold it at that temperature for t min to achieve remelting of the alloy material A and obtain melt B;

[0048] Please see Figure 2 , Figure 2 This diagram illustrates the refinement of the primary aluminum-rich phase during the remelting process of cast aluminum alloys. The heat treatment in this step is to remelt the solidified precipitates in the alloy material, causing partial remelting of the solidified precipitates in alloy material A, thereby achieving the goals of dendrite fragmentation, freeing, refinement, and homogenization of the precipitate structure. Furthermore, from... Figure 2 It can be seen that when heated to a temperature below the liquidus temperature of the primary aluminum-rich phase and held at that temperature, the primary aluminum-rich phase will undergo coarse dendrite fragmentation and transform into a fine equiaxed crystal structure under the action of solute and thermal diffusion.

[0049] To achieve the above effects, the temperature and time of the heat treatment in this step are not arbitrarily set. Instead, the influence of compositional gradient and interfacial energy on the morphology of the precipitated phase is considered collaboratively. A method is proposed to control the morphology and size of the solidified precipitated phase in cast aluminum alloy through remelting. That is, after the solidified phase precipitates, the system temperature is reheated to the gap between its solidus and liquidus temperatures by temperature control, and then held at this temperature gap. This causes the primary solid phase to become unstable, fragmented, and free under the influence of compositional gradient and interfacial energy, thereby refining the size of the precipitated phase and rounding the morphology of the primary phase. Therefore, the temperature T3 and time t of the heat treatment in this step are calculated using the following formulas:

[0050] T3 = T4 - m × (100 - C), t = (T4 - T3) / 6m; T4 is the melting point of pure aluminum, m is the average slope of the liquidus line of the primary aluminum-rich phase precipitation, and C is the percentage content of aluminum in the cast aluminum alloy.

[0051] The melting point of pure aluminum is 660℃, and the average liquidus slope m of the primary aluminum-rich phase precipitation in this embodiment is 7.5. The percentage content of aluminum element C in the cast aluminum alloy is 88. Therefore, in this embodiment, T3 = 660 - 7.5 × (100 - 88) = 570℃; t = (660 - 570) / (6 × 7.5) = 2 min.

[0052] Therefore, in this step, after heating alloy material A to 570℃, holding it at 570℃ for 2 minutes can achieve the remelting treatment of alloy material A.

[0053] Step 4: The melt B is cast and cooled to obtain alloy material B. The obtained alloy material B is a casting and alloy structure with optimized microstructure and properties, that is, the morphology of solidified precipitates in cast aluminum alloy is controlled.

[0054] Example 2

[0055] This embodiment takes Al-6Si cast aluminum alloy (94% aluminum by mass and 6% silicon by mass) as an example to provide a method for controlling the morphology of solidified precipitates in Al-6Si cast aluminum alloy by remelting, including the following steps:

[0056] Step 1: According to the composition percentage of Al-6Si cast aluminum alloy, that is, the ratio of 94wt.% aluminum and 6wt.% silicon, weigh the corresponding mass of aluminum ingots and crystalline silicon raw materials, melt them completely in the melting furnace, and hold them at a temperature of T1 = 700℃ for more than 10 minutes to obtain melt A.

[0057] Among them, the purity of aluminum ingots is ≥99.99%, and the purity of crystalline silicon is ≥99.99%;

[0058] Step 2: Cool the melt A to T2 = 565℃ and hold for 1 minute. During this process, the primary aluminum-rich phase (α-Al) and α-Al plus eutectic silicon precipitate and grow sequentially to obtain alloy material A.

[0059] Step 3: Heat the alloy material A to T3 and hold it at that temperature for t min to achieve remelting of the alloy material A and obtain melt B;

[0060] Where T3 = T4 - m × (100 - C) = 660 - 7.5 × (100 - 94) = 615℃, t = (T4 - T3) / 6m = (660 - 615) / (6 × 7.5) = 1min. Therefore, in this step, after heating alloy material A to 615℃, holding it at 615℃ for 1min can achieve the remelting treatment of alloy material A.

[0061] Step 4: Cast the remelted melt B to obtain castings and alloy structures with optimized microstructure and properties.

[0062] Comparative Example 1

[0063] The only difference between this comparative example and Example 1 is that:

[0064] This invention skips steps 2 and 3 and directly casts melt A to obtain alloy material.

[0065] Comparative Example 2

[0066] The only difference between this comparative example and Example 2 is that:

[0067] This invention skips steps 2 and 3 and directly casts melt A to obtain alloy material.

[0068] Experimental Section

[0069] (I) Microstructure analysis of alloys in Example 1 and Comparative Example 1

[0070] This invention tested and analyzed the alloy microstructure distribution and grain size distribution of the alloy material in Comparative Example 1, and the test results are as follows: Figures 3-5 As shown.

[0071] in, Figure 3 This is a micrograph of the multi-element alloy structure at a scale of 10 mm for the alloy material in Comparative Example 1. Figure 4 This is a photograph of the microstructure of the multi-element alloy at the 100 μm scale of the alloy material in Comparative Example 1. Figure 5 This is a grain size distribution diagram of the alloy material in Comparative Example 1.

[0072] The present invention tested and analyzed the alloy microstructure distribution and grain size distribution of alloy material B in Example 1, and the test results are as follows: Figures 6-8 As shown.

[0073] in, Figure 6 This is a micrograph of the multi-element alloy structure of alloy material B in Example 1 at a scale of 10 mm. Figure 7 This is a photograph of the microstructure of alloy material B in Example 1 at the 100 μm scale. Figure 8 This is a grain size distribution diagram of alloy material B in Example 1.

[0074] And by Figures 2-8 It can be seen that the grain size of the unremelted sample in Comparative Example 1 is concentrated in the range of 90 micrometers, which is 3 times the grain size of the remelted sample (the grain size is concentrated in the range of 30 micrometers).

[0075] (II) Microstructure analysis of alloys in Example 2 and Comparative Example 2

[0076] The present invention also tested the alloy microstructure distribution of the alloy materials prepared in Comparative Example 2 and Example 2, and the test results are as follows: Figure 9 , Figure 10 As shown.

[0077] Figure 9 This is a micrograph of the multi-element alloy structure at a scale of 10 mm for the alloy material in Comparative Example 2. Figure 10 This is a micrograph of the multi-element alloy structure of alloy material B in Example 2 at a scale of 10 mm.

[0078] And by Figures 9-10 It can be seen that the dendrite cell diameter of the unremelted sample in Comparative Example 2 is about 100 μm (circled area), while the cell diameter of the remelted sample in Example 2 is about 10 μm (circled area). Therefore, the grain cell diameter was refined by about 10 times after remelting.

[0079] Obviously, the above embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

Claims

1. A method for controlling the morphology of solidified precipitates in Al-Si hypoeutectic cast alloys through remelting, characterized in that, Includes the following steps: Step 1: After completely melting the raw materials for preparing the Al-Si hypoeutectic casting alloy, heat treatment is carried out at temperature T1 to obtain melt A; Wherein, T1>(T lid +50℃), T lid This is the liquidus temperature of the alloy; Step 2: Cool the melt A to T2 and then hold it at that temperature to obtain alloy material A; Where T2≤T sol T sol The solidus temperature of the alloy; Step 3: Heat the alloy material A to T3 and then hold it at that temperature. t min, so as to achieve the remelting treatment of the alloy material A to obtain melt B; Where T3 = T4 - m × (100 - C), t = (T4 - T3) / 6m; T 4 is the melting point of pure aluminum. m The average slope of the liquidus line for the precipitation of the primary aluminum-rich phase. C This represents the percentage content of aluminum in the cast aluminum alloy. Step 4: Cast the melt B and cool it to obtain alloy material B, which can realize the control of the solidification precipitate morphology in Al-Si hypoeutectic casting alloy. In step 1, the heat preservation treatment time is 10~30 minutes; In step 2, the heat preservation time is 0.5~1.5 min.

2. The method as described in claim 1, characterized in that, The Al-Si hypoeutectic casting alloy is either Al-12Si casting aluminum alloy or Al-6Si casting aluminum alloy.

3. The method as described in claim 2, characterized in that, When the Al-Si hypoeutectic cast alloy is an Al-12Si cast aluminum alloy, it consists of the following atomic mass percentage components: 88 wt.% Al and 12 wt.% Si.

4. The method as described in claim 2, characterized in that, When the Al-Si hypoeutectic cast alloy is an Al-6Si cast aluminum alloy, it consists of the following atomic mass percentage components: 94 wt.% Al and 6 wt.% Si.

5. The method as described in claim 1, characterized in that, The temperature of the casting process is T 3.

Images