CN115575398A

CN115575398A - Rapid detection method for cracks of magnesium alloy bar

Info

Publication number: CN115575398A
Application number: CN202211195987.8A
Authority: CN
Inventors: 黄礼新; 徐佐; 李蒙; 孔德才; 沈静茹; 朱利利; 张超; 郭浩鹏; 樊利国; 姚丹
Original assignee: CITIC Dicastal Co Ltd
Current assignee: CITIC Dicastal Co Ltd
Priority date: 2022-09-29
Filing date: 2022-09-29
Publication date: 2023-01-06

Abstract

A magnesium alloy bar crack rapid detection method comprises the following steps: cutting a bar to be detected into a bar section with a cross section thickness of 10 to 20mm; polishing the surface of one cross section of the bar stock slice, wherein the roughness of the cross section is kept below Ra3.2 mu m; uniformly coating solder paste on the smooth surface of the bar slice; heating the bar stock slices coated with the soldering paste in a heating furnace to 360 to 420 ℃, and keeping the temperature for 10 to 20min; taking out the mixture, air-cooling for 1 to 5 seconds, and then cooling in water at the temperature of 10 to 60 ℃. The method can quickly detect whether the casting crack exists in the bar stock, and does not need to be assisted by other detection methods; the paint is non-toxic and pollution-free, and cannot cause irreversible chemical injury to detection personnel; compared with the traditional cast rod casting crack detection method, the method is rapid; the detection process is simple, labor is saved, production cost is reduced, and production efficiency is improved.

Description

Method for rapidly detecting cracks of magnesium alloy bar

Technical Field

The invention relates to the technical field of bar stock detection, in particular to a magnesium alloy bar stock crack rapid detection method.

Background

The magnesium alloy is an alloy formed by adding other elements on the basis of magnesium. The method is characterized in that: the method has the advantages of small density (about 1.8 g/cm), high strength, large elastic modulus, good heat dissipation, good shock absorption, larger impact load bearing capacity than aluminum alloy, good process performance and good organic matter and alkali corrosion resistance. The method is mainly used in the industrial fields of automobiles, aviation, aerospace, transportation, rockets and the like. According to the forming process. Magnesium alloys can be classified into cast magnesium alloys and wrought magnesium alloys, which have great differences in composition and structure properties. The cast magnesium alloy is mainly used for automobile parts, machine part shells, electric components and the like; the cast magnesium alloy has the following characteristics: the crystallization temperature interval is large, the volume shrinkage and the linear shrinkage are large, the eutectic crystal volume, the specific heat capacity, the solidification latent heat, the density and the liquid pressure head in the structure are small, the fluidity is low, and the pulling crack and the shrinkage porosity tendency are generally much larger than those of the deformed aluminum alloy.

In the process of casting magnesium alloys, cracks are generally classified into hot cracks and cold cracks according to their formation processes. Cracks formed in the effective crystallization zone are called thermal cracks. Thermal cracking is a crack generated during solidification, and is a tendency to generate thermal cracking in an alloy having a wide crystallization temperature range formed in an effective crystallization temperature range from a linear shrinkage starting temperature to a solid phase point. The thermal cracks are mostly cracked along the grain boundaries, and the cracks are tortuous and irregular, and often branch, the surface is in oxidation color, and the macroscopic manifestations are surface cracks, central cracks, annular cracks, radial cracks and the like. The difficulty of shrinkage in the crystallization zone is a major cause of the occurrence of thermal cracking. The thermal crack sensitivity of the alloy can be reduced by reducing the temperature range of the brittle zone and reducing the difficult shrinkage factor in the brittle zone under given conditions. The high and low heat crack sensitivity of the alloy can be judged according to the plasticity A in the brittle zone and the linear shrinkage epsilon, namely the alloy sensitivity can be judged according to a temperature-plasticity diagram. A of more than 0.5% hardly causes thermal cracking. When A =0, it is called an absolute embrittlement region, and the probability of hot cracking approaches 100%. The upper limit of the brittleness of the alloy is less than or equal to the upper limit of the solid-liquid area, and the lower limit of the brittleness of the alloy is less than or equal to the lower limit of the solid-liquid area; the cold crack is a crack generated in a cooling process after solidification, and the cold crack mostly occurs in a temperature range of about 200 ℃. The surface of the cold crack is smooth and has no oxidation, and the cracks are mostly straight line side cracks, bottom cracks and splitting cracks in a crystal-crossing mode and are mostly cold cracks. Pure thermal cracks or cold cracks do not exist in the production process, most of the cracks are firstly generated, and then the thermal cracks develop into cold cracks in the cooling process, so that the bars are cracked. Cold cracks in the ingot form after solidification, due to difficulties in ingot shrinkage when the ingot is cooled below the unbalanced solidus temperature, i.e. depending on the magnitude of internal stresses and the magnitude of plasticity of the ingot at the time. Casting stress can be classified into thermal stress, phase transformation stress, and shrinkage resistance. In continuous casting, the phase transformation stress of the magnesium alloy can be disregarded, mainly the other two stresses, but the contraction force is not large and can be controlled, therefore, the thermal stress is the most dominant, so the cold crack depends on the magnitude of the thermal stress and the plasticity level inside the ingot in the solid state.

Casting cracks are cracks that form at higher temperatures that tend to occur in alloys with higher volume shrinkage and in castings with more complex shapes. When the casting is unreasonable in structural design and has a sharp corner, the transition arc of the thick and thin section at the joint is too small, the wall thickness difference is too large, and the like; the deformability of the casting mold or the sand mold (core) is poor, the fash is too large, and the setting of a core bone and a chill is improper to prevent shrinkage; impurities or additives for promoting crack formation exist in the magnesium alloy, and the magnesium alloy is not good in deterioration or fails in deterioration, so that grains are large and the properties become brittle; the pouring system is improperly arranged, and the vicinity of an inner pouring gate or the root of a large riser is seriously overheated; the sand mold pouring temperature is too high; grooving and taking out the casting too early after the sand casting is poured; the heat treatment is overheated or over-burnt, and the cooling speed is over-excited. In order to save production cost, a production line usually cuts off a visible crack part, and the rest part is extruded to prepare an associated extrusion rod, but because the cut part may be difficult to observe by visual and conventional means, too precise instruments such as metallographic microscopic observation can be found, but the efficiency is too low, so that the production line is usually difficult to adopt. The extruded bar is welded with partial cracks, excavation is more difficult to find in appearance, only in the subsequent forging process, the cracks of the bar can be further shown, so that the product is invalid, the concealment of the cracks is strong, and forging resources are wasted.

Cracking often occurs during production. Because the existence of the cracks damages the continuity of the metal structure, the metal structure cannot be pressed in the subsequent production processes of extrusion, rolling and the like, and the production efficiency, the quality of finished products and the economic efficiency are seriously influenced. The crack detection of the bar before production is of great importance to the quality of magnesium alloy casting products. The existing crack detection technology mainly comprises a developer detection method, an eddy current detection method and an ultrasonic detection method.

The developer detection method is a method in which a dye-permeable liquid or a fluorescent-permeable liquid (hereinafter referred to as "liquid-permeable liquid") having a high permeability in which a dye is dissolved is attached to the surface of an object to be inspected, and then penetrates into an opening defect, and thereafter, a thin layer (hereinafter referred to as "developer layer") of inorganic white powder (hereinafter referred to as "developer" by those skilled in the art) such as magnesium carbonate powder or calcium carbonate powder is formed on the surface of the object to be inspected, and the liquid-permeable liquid penetrating into the opening defect is sucked out to the surface of the developer layer through the developer layer to present a defect indication pattern. The developer detection method has a problem that it is difficult to know a coated portion before drying and to form a uniform developer layer when a coating operation must be performed quickly. When the developer layer is not uniform, the gaps between the developing material particles are not uniform, or a portion where no gap is present, the immersion liquid is unevenly sucked or is not sucked at all, and therefore, it is difficult to accurately detect the position or size of the opening defect portion. Industrial nondestructive inspection produces radiation, which in large quantities may be sterile or even carcinogenic.

Eddy current testing is one of many NDT (non-destructive testing) methods that use the basic theory of H-electromagnetics as the basis for conductor testing. The generation of eddy currents results from a phenomenon known as electromagnetic induction. When an alternating current is applied to a conductor, such as a copper wire, the magnetic field will generate a magnetic field within the conductor and in the space surrounding the conductor. Eddy currents are induced currents that flow in a loop. This is called a vortex because it is in the same form that a liquid or gas flows in a loop around an obstacle. If a conductor is placed in the changing magnetic field, eddy currents will be generated in that conductor, and eddy currents will also generate their own magnetic field, which expands as the alternating current rises and blanks as the alternating current decreases. Therefore, when defects appear on the surface or the near surface of the conductor or some properties of the measured metal material are changed, the intensity and the distribution of the eddy current are influenced, so that the change condition of the eddy current can be detected together, and the existence of the defects in the metal and the change of the metal performance can be indirectly known. The device is only suitable for detecting the surface and near-surface defects of the workpiece, and can not detect the internal defects of the deep layer of the workpiece; it is also difficult to characterize and quantify defects.

Ultrasonic flaw detection is a nondestructive testing method for detecting internal flaws of materials by using the difference of acoustic properties of the materials and the flaws thereof on the energy changes of ultrasonic wave propagation waveform reflection conditions and penetration time. The pulse reflectometry uses a longitudinal wave for vertical flaw detection and a transverse wave for oblique flaw detection. The pulse reflection method includes longitudinal wave flaw detection and transverse wave flaw detection. On an oscillographic screen of the ultrasonic instrument, the propagation time of the sound wave is represented by an abscissa, and the amplitude of the echo signal is represented by an ordinate. For the same homogeneous medium, the propagation time of the pulse wave is proportional to the acoustic path. The presence of a defect can therefore be judged from the occurrence of a defect echo signal; the distance between the defect and the detection surface can be determined according to the position of the echo signal, so that defect positioning is realized; and judging the equivalent size of the defect through the echo amplitude. The ultrasonic flaw detection method has smooth requirements on the working surface, requires experienced inspectors to distinguish the types of the defects, and has no intuition on the defects.

Disclosure of Invention

In view of the above, the present invention aims to provide a method for rapidly detecting cracks of magnesium alloy bars, which is used for detecting casting crack defects of magnesium alloy bars (cast bars and extruded bars). The method is suitable for detecting the cracks of the magnesium alloy bar. The detection method is non-toxic and pollution-free; the method is not assisted by other detection methods; the detection period is short; the method is simple and easy to operate; the manpower is saved, and the production efficiency is improved.

In order to achieve the purpose, the technical scheme of the invention is realized as follows:

a magnesium alloy bar crack rapid detection method comprises the following steps: cutting a bar to be detected into a bar section with a cross section with the thickness of 10-20mm; polishing the surface of one cross section of the bar stock slice, wherein the roughness of the cross section is kept below Ra3.2 mu m; uniformly coating solder paste on the smooth surface of the bar slice; putting the bar stock slices coated with the soldering paste into a heating furnace, heating to 360-420 ℃, and keeping the temperature for 10-20min; taking out the mixture, air-cooling for 1 to 5 seconds, and then cooling in water at the temperature of 10 to 60 ℃.

In some embodiments, the method further comprises a visual observation step, wherein the soldering paste penetrating into the cracks of the bar stock section solidifies again, oxidizes and presents a color different from that of the metal, and the surface of the section is visually observed for identification.

In some embodiments, the front section, the middle section and the end section of the bar material to be detected are respectively cut into cross section slices with the thickness of 10-20 mm for detection.

In some embodiments, the furnace comprises an induction furnace.

According to the invention, the bar stock is coated with the tin paste, the bar stock is heated, expands with heat and contracts with cold, the magnesium alloy metal expands, if cracks exist, molten tin liquid flows in, the molten tin liquid is solidified after cooling, the cracks are further expanded, the magnesium alloy shows metal luster with different colors, the magnesium alloy shows lines with certain degrees along the cracks, and whether the cracks are formed or not and the forms of the cracks can be easily detected through visual observation.

Compared with the prior art, the magnesium alloy bar crack rapid detection method has the following advantages:

1. the method can quickly detect whether the cast crack exists in the bar stock, and can find whether the cast crack, the crack and the like exist after the bar stock is placed for several days compared with the traditional cast bar.

2. Casting cracks of the extrusion rod can also be detected by the method, but other conventional methods cannot be detected due to extrusion welding (one of the largest bright spots is detection of the extrusion welding cracks of the extrusion rod).

3. The method can visually observe the surface quality without other detection methods for auxiliary detection.

4. The method is non-toxic and pollution-free, and does not cause irreversible chemical damage to detection personnel.

5. The method can simplify the detection process, save labor and improve productivity.

Drawings

The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate an embodiment of the invention and, together with the description, serve to explain the invention and not to limit the invention. In the drawings:

FIG. 1 is a flow chart of the present invention.

FIG. 2 is a schematic view of a section of a bar to be tested according to the present invention.

Description of the reference numerals

1-slicing a bar stock; 2-bar stock to be detected.

Detailed Description

It should be noted that the embodiments and features of the embodiments may be combined with each other without conflict.

The technical solutions of the present invention will be described below clearly and completely with reference to the accompanying drawings and embodiments, and it is to be understood that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

The method for rapidly detecting cracks of a magnesium alloy bar according to an embodiment of the present invention is described below with reference to fig. 1 to 2 in combination with the embodiment.

A magnesium alloy bar crack rapid detection method comprises bar sampling; grinding the sample block; coating a material paste; induction heating; cooling; and (4) carrying out visual observation. Cooling a casting rod 2 to be detected after drawing casting, and respectively cutting a cross section bar stock slice 1 with the thickness of 10-20 mm at the front section, the middle section and the tail section of the cooled casting rod; polishing the surface of one cross section of the bar section 1, wherein the roughness of the cross section is kept below Ra3.2 mu m; uniformly coating solder paste on the smooth surface of the slice; placing the bar stock slice 1 coated with the soldering paste into an induction heating furnace, heating to 360-420 ℃, and keeping the temperature for 10-20min; and melting and penetrating the solder paste into the cracks, taking out the solder paste, cooling in air for 1 to 5 seconds, immediately cooling in water at the temperature of 10 to 60 ℃, solidifying and oxidizing the solder paste penetrating into the cracks of the bar section 1 again, presenting a color different from that of the metal, presenting a certain crack propagation rule, and visually observing and identifying the surfaces of the sections. The surface is observed microscopically from a crack area, the crack is formed at the initial heating or heating stage, under the condition of rapid heating, a large temperature difference is generated inside and outside the continuous casting billet to form thermal stress, the surface of the continuous casting billet generates tensile stress by rapid heating, when the crack is on the surface or near the surface of the bar slice 1, the tensile stress on the surface of the casting rod enables the continuous casting billet to generate stress concentration in a microcrack area, the formed microcracks can be connected and expanded, simultaneously, through induction heating, the skin effect can be formed on the surface, the tin paste on the surface of the casting rod is melted into liquid at high temperature and permeates into the crack, the oxidation discoloration is carried out at high temperature, and obvious crack lines can be clearly seen after cooling. Most of the hot cracks of the forging die parts appear in the final solidification region of the product, the columnar crystal region of the tissue near the crack is shorter, and the columnar crystal region far away from the crack is longer; the invention can detect the extrusion welding cracks which are difficult to detect by the existing detection method. When the extrusion process conditions of the extrusion rod are not proper, the product is welded badly, so that the mechanical property of the welding seam is poor, the strength of the extrusion welding seam is lower than that of the base metal, and the longitudinal cracks and the layering phenomenon appear at the welding seam of the extrusion rod. The method can detect the welding cracks, does not need other detection methods to assist in detection, has short detection period and improves the production efficiency.

Referring to fig. 1, the invention provides a rapid detection method for crack defects of magnesium alloy bars, which is used for detecting casting crack defects of the magnesium alloy bars. Cooling the cast rod after drawing casting, and cutting sample slices into cross-section slices with the slice thickness of 10-20mm at the front section, the middle section and the tail section of the cooled cast rod respectively as shown in figure 2; fixing the fixture for slicing on a numerical control machine, polishing the surface of the cross section of the slice to the roughness below Ra3.2 mu m, and taking down the slice on the numerical control machine; uniformly coating solder paste on the smooth surface of the slice; putting the slices coated with the soldering paste into an induction heating furnace through a feeding frame, heating to 360 to 420 ℃, and keeping the temperature for 10 to 20min; and taking out the slices through a feeding frame, air-cooling for 1 to 5 seconds, immediately cooling in water at 10 to 60 ℃, melting and permeating the solder paste into cracks, then solidifying the solder paste in the presence of the cold, wherein the cracks have a color different from that of the metal and a certain crack propagation rule, and visually observing the surfaces of the slices and identifying the cracks.

Compared with the prior art, the method for rapidly detecting the cracks of the magnesium alloy bar has the following advantages:

1. the method can quickly detect whether the casting crack exists in the bar stock, and can find whether the casting crack, the crack and the like exist after the bar stock is placed for several days compared with the traditional bar casting.

2. Casting cracks of the extrusion rod can also be detected by the method, but other conventional methods cannot detect the casting cracks because of extrusion welding (one of the largest bright spots is detection of the extrusion welding cracks of the extrusion rod).

5. The method can simplify the detection process, save manpower and improve productivity.

In the description of the present invention, it is to be understood that the terms "central," "longitudinal," "lateral," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," and the like are used in the orientations and positional relationships indicated in the drawings, which are based on the orientation or positional relationship shown in the drawings, and are used for convenience of description and simplicity of description only, and are not intended to indicate or imply that the referenced devices or elements must have a particular orientation, be constructed and operated in a particular orientation, and thus, are not to be construed as limiting the scope of the present invention.

Furthermore, the terms "first", "second" and "first" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of the present invention, "a plurality" means at least two, e.g., two, three, etc., unless specifically limited otherwise.

In the present invention, unless otherwise expressly stated or limited, the terms "mounted," "connected," "secured," and the like are to be construed broadly and can, for example, be fixedly connected, detachably connected, or integrally formed; may be mechanically, electrically or otherwise in communication with each other; either directly or indirectly through intervening media, either internally or in any other relationship. The specific meanings of the above terms in the present invention can be understood according to specific situations by those of ordinary skill in the art.

The present invention is not limited to the above preferred embodiments, and any modifications, equivalent substitutions, improvements, etc. within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A magnesium alloy bar crack rapid detection method is characterized by comprising the following steps: cutting a bar to be detected into a bar section with a cross section with the thickness of 10-20mm; polishing the surface of one cross section of the bar section, wherein the roughness of the cross section is kept below Ra3.2 mu m; uniformly coating solder paste on the smooth surface of the bar slice; putting the bar stock slices coated with the soldering paste into a heating furnace, heating to 360-420 ℃, and keeping the temperature for 10-20min; taking out the mixture, air-cooling for 1 to 5 seconds, and then cooling in water at the temperature of 10 to 60 ℃.

2. The method for rapidly detecting the cracks of the magnesium alloy rod according to claim 1, characterized by further comprising a visual observation step, wherein the soldering paste which penetrates into the cracks of the rod is solidified and oxidized again and presents a color different from that of the metal, and the surface of the slice is visually observed for identification.

3. The method for rapidly detecting cracks in a magnesium alloy rod according to claim 1, wherein the front section, the middle section and the end section of the rod to be detected are respectively cut into cross section slices with the thickness of 10-20mm for detection.

4. The method for rapidly detecting cracks in the magnesium alloy rod according to claim 3, wherein the heating furnace comprises an induction heating furnace.