Method for preparing heterostructure magnesium alloy based on low-temperature friction stir additive

Abstract

The invention relates to a method for preparing a heterostructure magnesium alloy based on low-temperature friction stir additive in the field of metal processing, and designs a high-quality and high-efficiency cooling tool, which mainly comprises the following steps: firstly, cooling alcohol to low temperature by using liquid nitrogen; then the magnesium alloy plate to be machined is fixed to a cooling tool in a lap joint mode, and the tool mainly comprises a device body (1), a cooling liquid inflow hole (2), a cooling liquid outflow hole (3), a workpiece containing groove (4), a liquid storage chamber (5), a pressing plate (6) and fastening screws (7); then low-temperature alcohol is introduced, an advancing path and technological parameters are set, first-layer stirring friction additive manufacturing is conducted, and in the machining process, a stirring head and a workpiece are always kept to be submerged in cooling liquid; then, the surface obtained after material adding is milled to be flat, a layer of plate is overlaid on the other unmachined surface again, and the plate is fixed into the workpiece containing groove; and finally, second-layer friction stir additive manufacturing is conducted on the other face of the plate according to the same parameters and the same path. The method can be suitable for additive manufacturing of low-melting-point metal such as magnesium alloy and aluminum alloy at the same time, the multi-scale gradient heterostructure magnesium alloy can be prepared at the same time, the preparation efficiency is improved, and high-quality and low-cost preparation of heterostructure materials is achieved.

Description

Technical Field

[0001] The invention belongs to the field of metal processing, and in particular to a method for preparing a heterogeneous structure magnesium alloy based on low-temperature friction stirring additive. Background Art

[0002] Additive manufacturing, as a new material forming process, has developed rapidly in recent years. However, processes such as laser additive manufacturing and arc additive manufacturing are accompanied by material melting and solidification processes, which may cause defects such as pores and cracks for magnesium alloys and aluminum alloys with active chemical properties. Adding protective gas will significantly increase manufacturing costs.

[0003] Friction stir additive manufacturing is a solid-phase additive manufacturing process that has received widespread attention in recent years. At present, the main friction stir additive methods include rod friction deposition and wire feeding additive. However, due to the expensive equipment manufacturing and complex additive process, it is difficult to put them into practical application in a short period of time. Friction stir processing, as a solid-phase processing technology derived from friction stir welding, has the same material forming principle as friction stir additive manufacturing. This means that additive manufacturing can be achieved directly by friction stir processing stacked plates. Such a process is both efficient and economical, and is very suitable for the preparation of layered heterostructured magnesium alloys with excellent mechanical properties.

[0004] At present, there are few methods for preparing heterogeneous magnesium alloys by stir friction additive manufacturing. Prior art 1 (a method for preparing heterogeneous magnesium alloy sheets, application number: 202310443997.7) prepares heterogeneous magnesium alloys by smelting. This method has a simple structure and is easy to operate, which can effectively prepare heterogeneous magnesium alloys. However, the preparation temperature of this method is relatively high, the overall grain size of the prepared magnesium alloy is relatively large, and the mechanical properties are easily affected.

[0005] Prior art 2 (a method for preparing a heterogeneous magnesium alloy, application number: 202410034408.4) provides a method for preparing a heterogeneous magnesium alloy by rolling, first cutting the magnesium alloy sheet into a shape with a bulging middle, then performing annealing and heating processes, then quickly taking it out and performing high-temperature rolling, and finally performing secondary annealing. Although this method can prepare a large range of heterogeneous structural areas, the process is complicated and the process is accompanied by a high temperature, which is not conducive to grain refinement.

[0006] Therefore, it has become an urgent task to design a preparation method that can simultaneously achieve efficient preparation of heterostructured metals to the greatest extent, maximize product quality, and be easily automated. Summary of the invention

[0007] In view of the problems existing in the current preparation of heterogeneous structure magnesium alloys, the purpose of the present invention is to provide a method for preparing heterogeneous structure magnesium alloys based on low-temperature stir friction additive, and designs a low-temperature stir friction additive tooling with a simple structure and easy installation. The device can reduce the temperature of the workpiece during stir friction additive, refine the grains, and eliminate the heat affected zone in the manufacturing area by cooling the welded workpiece during manufacturing.

[0008] The present invention is a method for preparing a heterogeneous structure magnesium alloy based on low temperature friction stir additive, which specifically comprises the following steps:

[0009] 1. A method for preparing a heterogeneous structure magnesium alloy based on low temperature friction stir additive, characterized in that it specifically comprises the following steps:

[0010] Step 1: Use liquid nitrogen to cool the alcohol to a low temperature, and clamp the tooling body (1) firmly;

[0011] Step 2: placing the alloy plate to be processed in the workpiece placement groove (4), and tightening the pressing plate (6) with the fastening screws (7) to ensure that the plate to be processed is reliably fixed;

[0012] Step 3: Connect the drainage hole (2) and the water outlet hole (3) to pipes respectively, and inject low-temperature alcohol into the liquid storage chamber (5) from the coolant inlet hole. Ensure that the alcohol always submerges the workpiece (11) and the stirring head (8) by adjusting the coolant inflow and outflow rates:

[0013] Step 4: Setting the travel path (9) and process parameters for the first layer of friction stir additive manufacturing;

[0014] Step 5: The obtained plate surface is milled flat and the second layer of additive manufacturing is performed with the same path and process parameters.

[0015] 2. Further, in step 1, liquid nitrogen needs to cool the alcohol to -95 to -100 °C before the experiment to ensure high cooling efficiency;

[0016] 3. Further, in step 2, the workpiece (11) is a lapped structure consisting of a 3 mm thick magnesium alloy sheet stacked on a 1.5 mm thick magnesium alloy sheet; all fastening screws (7) are M8 screws, and all screw holes (10) are M8 screw holes;

[0017] 4. Further, in step 3, the coolant inlet (2) and the coolant outlet (3) are both connected to a dedicated low-temperature resistant pipe, and a valve is provided on the pipe to control the liquid flow rate, and the low-temperature alcohol is injected into the pipe through a water pump and flows into the liquid storage chamber (5);

[0018] 5. Further, in step 4, the travel path of the stirring head (8) is "S" shaped, and the manufacturing directions of two adjacent passes are opposite and the interval is the diameter of the stirring needle;

[0019] 6. Further, in step 5, the milled and flattened machined surface is placed in the groove and a 1.5 mm thick magnesium alloy sheet is re-stacked on the surface to perform the second layer of friction stir additive manufacturing, and the motion trajectory completely overlaps with the first layer;

[0020] The tooling body is clamped on the workbench by a common clamp;

[0021] The tooling is made of 45 steel, the screws are made of stainless steel, and the pipes are low-temperature resistant steel wire hoses.

[0022] Beneficial Effects

[0023] 1. The advantages of the present invention are simple structure and low manufacturing difficulty. It can be completed in an ordinary small workshop. It is not only suitable for stir friction additive manufacturing experiments in the laboratory, but also can batch manufacture multiple tooling to facilitate batch production of stir friction additive products. It is also low-cost and simple to operate manually during the experiment.

[0024] 2. Compared with the prior art, the method of the present invention is simple, the tooling is easy to install, and the coolant can be freely selected from environmentally friendly coolants such as normal temperature water, low temperature water, low temperature alcohol, liquid nitrogen, etc. according to the needs, and there is no pollution during the processing. The coolant covers the workpiece surface and the stirring head at the same time, the workpiece has a large effective cooling area, a fast cooling rate, and refines the grains, protecting the performance of the workpiece itself, reducing the processing cost, and can also eliminate the heat-affected zone and improve the quality of the processing area.

[0025] 3. Currently, there are few public inventions on the preparation of heterogeneous structural materials by multilayer friction stir additive manufacturing, and there are not many designs for cooling tooling for friction stir additive manufacturing. Although there are some methods that can prepare high-quality heterogeneous magnesium alloys, the complexity of their structures and processes not only increases the economic cost, but also increases the time cost, making it difficult to meet actual production needs. The present invention only needs to use a CNC milling machine to process the cubic material into a liquid storage chamber, a workpiece placement groove, a screw hole, a drainage hole, and a water outlet according to the drawings to complete the manufacture of the fixture body. The clamping and disassembly during the experiment are simple, which greatly improves the experimental efficiency and processing stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is a schematic diagram of the preparation method of the present invention;

[0027] Figure 2 It is a schematic diagram of the cooling tooling of the present invention;

[0028] Figure 3 It is a schematic diagram (disassembled diagram) of the cooling tooling of the present invention;

[0029] Figure 4The surface and cross-sectional morphology of the symmetrical layered heterostructure magnesium alloy prepared by low-temperature friction stir additive manufacturing in Example 1 of the present invention;

[0030] In the figure, 1-device body, 2-drainage hole, 3-water outlet hole, 4-workpiece placement groove, 5-liquid storage chamber, 6-pressure plate, 7-M8 fastening screw, 8-stirring head, 9-stirring head movement path, 10-M8 screw hole, 11-workpiece, 12-clamping end. DETAILED DESCRIPTION

[0031] Example 1

[0032] In this embodiment, the material to be processed is AZ31 magnesium alloy, the size of the magnesium alloy plate stacked on the upper layer is 120×140×1.5mm, and the size of the magnesium alloy in the middle is 120×140×3mm. Before the experiment, a cooling tool suitable for the material size was processed using 45 steel. The specific experimental steps are as follows:

[0033] Step 1: Use liquid nitrogen to cool the alcohol to -95 to 100°C, and fix the tool body (1) on the workbench of the stir friction welding machine modified from a CNC machine tool, and use a common clamp to clamp the clamping end (12) to ensure reliable fixation of the tool body;

[0034] Step 2: Place the AZ31 plate to be processed in the workpiece placement slot (4) of the cooling fixture, with the thickness of the upper plate being 1.5 mm and the thickness of the lower plate being 3 mm, and then tighten the pressing plate (6) using the fastening screws (7) to ensure that the plate to be processed is reliably fixed, and all the M8 screws are tightened;

[0035] Step 3: The coolant inflow hole (2) and the coolant outflow hole (3) are connected to pipelines respectively, and valves are installed on the pipelines to control the water flow rate. Then, a water pump is used to inject low-temperature alcohol into the liquid storage chamber (5) from the drainage hole. By adjusting the coolant inflow and outflow rates, it is ensured that the alcohol always submerges the workpiece (11) and the stirring head (8);

[0036] Step 4: Assemble the stirring head (8) with a conical stirring needle with a bottom diameter of 6 mm, a top diameter of 4 mm, and a height of 1.8; set the travel path (9) to an "S" shape (such as Figure 1 As shown), reciprocate in the extension direction for 5 times, set the rotation speed to 1000r / min with an interval of 4mm, the stirring head travel speed to 100mm / min, the shoulder pressure to 0.2mm, and start the first layer of additive manufacturing;

[0037] Step 5: After the program is completed, the upper layer of 1.5mm and 3mm thick AZ31 additive manufacturing is completed, and the size of the manufactured area is about 100×20×1.6mm; the surface of the obtained plate is milled flat, and a layer of 1.5mm thick AZ31 plate is superimposed on the other side of the 3mm plate. The second layer of additive manufacturing is carried out with the same path and process parameters, and its movement path completely overlaps with the manufacturing path of the first layer. The obtained gradient structure is as follows Figure 4 As shown, the upper and lower layers of the processing area are ultrafine grain areas, the subsurface layer is a fine grain area, and the middle layer retains the coarse grain area of ​​the parent material.

Claims

1. A method for preparing a heterogeneous structure magnesium alloy based on low temperature friction stir additive, characterized in that: The specific steps include: Step 1: Use liquid nitrogen to cool the alcohol to a low temperature, and clamp the tooling body (1) firmly; Step 2: placing the alloy plate to be processed in the workpiece placement groove (4), and tightening the pressing plate (6) with the fastening screws (7) to ensure that the plate to be processed is reliably fixed; Step 3: The drainage hole (2) and the water outlet hole (3) are connected to pipes respectively, and low-temperature alcohol is injected into the liquid storage chamber (5) from the coolant inflow hole, and the coolant inflow and outflow rates are adjusted to ensure that the alcohol always submerges the workpiece (11) and the stirring head (8); Step 4: Setting the travel path (9) and process parameters for the first layer of friction stir additive manufacturing; Step 5: The obtained plate surface is milled flat and the second layer of additive manufacturing is performed with the same path and process parameters.

2. The method for preparing heterogeneous structure magnesium alloy based on low temperature friction stir additive according to claim 1, characterized in that: In step 1, liquid nitrogen needs to cool the alcohol to -95 to -100 °C before the experiment to ensure high cooling efficiency.

3. The method for preparing heterogeneous structure magnesium alloy based on low temperature friction stir additive according to claim 1, characterized in that: In step 2, the workpiece (11) is a lapped structure consisting of a 3 mm thick magnesium alloy plate and a 1.5 mm thick magnesium alloy plate stacked on top of each other; all the fastening screws (7) are M8 screws, and all the screw holes (10) are M8 screw holes.

4. The method for preparing heterogeneous structure magnesium alloy based on low temperature friction stir additive according to claim 1, characterized in that: In step 3, the coolant inlet hole (2) and the coolant outlet hole (3) are both connected to a dedicated low-temperature resistant pipe, and a valve is provided on the pipe to control the liquid flow rate. The low-temperature alcohol is injected into the pipe through a water pump and flows into the liquid storage chamber (5).

5. The method for preparing heterogeneous structure magnesium alloy based on low temperature friction stir additive according to claim 1, characterized in that: In step 4, the travel path of the stirring head (8) is "S" shaped, and the manufacturing directions of two adjacent passes are opposite and the interval is the diameter of the stirring needle.

6. The method for preparing heterogeneous structure magnesium alloy based on low temperature friction stir additive according to claim 1, characterized in that: In step 5, the milled and flattened surface is placed on the lower layer and a 1.5 mm thick magnesium alloy sheet is re-overlaid to perform the second layer of friction stir additive manufacturing, and the motion trajectory completely overlaps with the first layer; The tooling body is clamped on the workbench by a common clamp; The tooling is made of 45 steel, the screws are made of stainless steel, and the pipes are low-temperature resistant steel wire hoses.

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