Hot isostatic pressing method for relieving low plasticity of selective laser melting (SLM) magnesium alloy

Abstract

The invention belongs to the field of alloy materials, and relates to a hot isostatic pressing method for improving low plasticity of a selective laser melting (SLM) magnesium alloy. The hot isostaticpressing method comprises five steps of printing, powder spreading, laser scanning, hot isostatic pressing and cooling. Before printing, a forming cavity is filled with high-purity argon to ensure that the oxygen content is less than 10 ppm; and during printing, the temperature of the forming cavity is kept between 30-40 DEG C. An equivalent magnesium alloy material is used as a base plate for powder spreading, a zigzag scanning strategy is adopted for a powder layer with a laser beam, and after the laser beam scans the powder layer, a powder feeding device continues to spread powder on the layer; the laser beam is rotated by 90 degrees clockwise in the scanning direction, and the powder on the layer is melted; and the subsequent layer preparation process is repeated until the preset product height is reached. The hot isostatic pressing method is simple in process flow, stable in process parameters, and a high-strength and high-plasticity AZ61 magnesium alloy can be produced under theprotection of conventional argon, and the elongation is 77%-160% higher than that of an SLM state. The production efficiency is high, and the powder is low in cost and easy to prepare, so that the production cost and difficulty can be effectively reduced. The hot isostatic pressing method is easy to operate and realize.

Description

technical field [0001] The invention belongs to the field of alloy materials and relates to a hot isostatic pressing method for improving the low plasticity of selective laser melting magnesium alloys. Background technique [0002] Magnesium is widely used in automobile manufacturing, aerospace, medicine and many other fields due to its light weight, high specific strength and other characteristics to adapt to the purpose of green materials and green development. my country has also listed it as a key project. In order to promote the rational development and utilization of magnesium resources, the country has listed "magnesium alloy application and industrialization" as a major special project of the "Tenth Five-Year Plan" research project, and "advanced" in the "863" science and technology plan. Magnesium Alloy and Application Technology" is listed as the key topic of the special project "High Performance Structural Materials Technology" in the field of new materials technol...

AI Technical Summary

Problems solved by technology

[0006] At present, the research on the preparation of metal samples by selective laser melting is mostly focused on stainless steel, nickel-based alloys, aluminum alloys, titanium alloys, etc. Due to the special physical properties of magnesium alloys, the research process is relatively difficult, so related research is still in its infancy.

For example, magnesium alloy powder is easy to oxidize, and it is easy to cause combustion during preparation; magnesium alloy has a low melting point and is easy to vaporize. The appropriate printing parameter settings need to be determined, and there are many parameters that need to be considered during molding, such as laser power, laser scanning, etc. Speed, powder layer thickness, scanning strategy, scanning distance, etc., but if the laser power is too high, the powder will be overburned or even evaporated. If the scanning distance is too large, adjacent laser scanning tracks cannot be overlapped, which will seriously affect the layer density, leading to defects in subsequent molding

In addition, magnesium alloys are soft and difficult to prepare samples, which also limits the research progress of selective laser melting of magnesium alloys to a certain extent.

[0007] In the prior art, in the selective laser melting preparation of magnesium alloys, there are two problems in the sample while the strength is improved: the first is the problem of poor plasticity, document 1 (Mater.Sci.Eng.A 611(2014): 212 -222), the strength of the magnesium alloy sample prepared by SLM is relatively high. While the ultimate tensile strength is 296MPa and the yield strength is 254MPa, the plastic elongation is only 1.24%-1.83%.

On the one hand, refined grains are formed by rapid solidification. According to the Hall-Petch formula, the strength increases after the grains are refined, but the microstructure shows that the second phase Mg 17 al 12 Precipitation along grain boundaries, softer magnesium matrix and brittle hard second phase Mg 17 al 12 The two-phase interface of the two phases will become the source of cracks during stretching, which will cause fracture during stretching, resulting in poor plasticity

[0008] Second, the problem of porosity

Pore ​​defects are also a major reason for limiting the plasticity of materials

[0009] At present, the research on the performance of AZ61 magnesium alloy prepared by SLM is still relatively limited. The existing technology can solve the problem of high strength, but due to the nature of SLM forming when no alloying elements are added, it is unavoidable that the second phase precipitates at the grain boundary and limits the plasticity. , porosity also appears along with the forming process

And it is worth noting that there is no research and technology on the density and plasticity of SLM magnesium alloys.

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