1. A method for evaluating the hot cracking tendency of cast magnesium alloy is characterized by comprising the following steps: simulating an actual casting process to prepare an eccentric hollow cylindrical casting, measuring and counting the total length L of surface cracks of the casting after the casting is poured, representing the coefficient of thermal cracking tendency of the alloy by utilizing the product C of the total length L of the surface cracks of the eccentric hollow cylindrical casting and the wall thickness ratio R, wherein the larger the value C is, the larger the thermal cracking tendency of the alloy is represented, wherein:

wall thickness ratio

The coefficient of thermal cracking tendency C ═ lxr;

the eccentric hollow cylinder is of a cylindrical structure with a circular through hole in the axial direction, the diameter of the outer circle of the cross section of the eccentric hollow cylinder is phi 1, the diameter of the inner hole is phi 2, and the distance between the circle center of the outer circle and the circle center of the inner hole is the eccentricity m.

2. The method for evaluating the heat cracking tendency of a cast magnesium alloy according to claim 1, wherein: the height H of the eccentric hollow cylinder is 10-100 mm, the diameter phi 1 of the outer circle is 10-50 mm, the size range of the diameter phi 2 of the inner hole is 0.5 phi 1-0.8 phi 1, the size range of the eccentricity m is 0.04 phi 1-0.1 phi 1, and when m is equal to 0.1 phi 1, the phi 2 can not be 0.8 phi 1.

3. The method for evaluating the heat cracking tendency of a cast magnesium alloy according to claim 1, wherein: an eccentric hollow cylindrical casting is prepared by adopting a sand mold process.

4. The method for evaluating the heat cracking tendency of a cast magnesium alloy according to claim 1, wherein: the pouring temperature of the eccentric hollow cylindrical casting is 620-700 ℃.

5. The method for evaluating the heat cracking tendency of a cast magnesium alloy according to claim 1, wherein: when different alloy hot cracking tendencies are compared, the eccentric hollow cylindrical casting adopts the same height, the same excircle diameter, the same inner hole diameter and the same eccentricity.

6. The method for evaluating the heat cracking tendency of a cast magnesium alloy according to claim 1, wherein: the cast magnesium alloy is one of Mg-Zn system, Mg-Al system, Mg-Ca system, Mg-Zn-Zr system, Mg-Zn-Y system, Mg-Al-Ca system and Mg-Gd-Y system.

Background

The magnesium alloy has lighter weight and higher specific strength, so the magnesium alloy is widely applied to the fields of aerospace, automobile industry and other civil products. Magnesium alloy parts are generally prepared by adopting a casting process, and because the magnesium alloy has large shrinkage, hot cracking defects are easily generated in the casting forming process. The hot cracking defect is one of the most serious defects of the casting, and the extremely small micro-cracks can greatly reduce the service life of the part and even lead the part to be directly scrapped, so the hot cracking resistance of the cast magnesium alloy is a key index for mass production of the casting.

Generally, when the temperature is slightly higher than the solidus temperature, hot cracking defects are often generated in a hot spot region where the casting solidifies or a position where the sectional area changes greatly under the effect of shrinkage stress. Thermal cracks generally consist of primary cracks and secondary cracks distributed along intergranular paths. A large number of researches show that heat cracking is a complex phenomenon, the influence factors are more, and the heat cracking tendency of the alloy cannot be comprehensively evaluated due to a single reason.

There are many thermal cracking evaluation methods, such as ring test, constraint bar, instrumental measurement, in situ evaluation, etc. In these methods, there are some advantages and disadvantages. At present, the most applied methods in production are a ring test method, a restraint bar method and the like, and although the test result is not very accurate, the method is very intuitive in actual production and has certain practicability. How to directly and accurately reflect the hot cracking tendency of castings with different alloys and different structures is still a problem which needs to be solved urgently in the current production.

Disclosure of Invention

The invention aims to provide an evaluation method of the heat cracking tendency of a cast magnesium alloy, which accurately reflects the heat cracking tendency of the alloy and is used for evaluating the engineering capability of the cast alloy.

The technical scheme of the invention is as follows:

a method for evaluating the hot cracking tendency of cast magnesium alloy is characterized by comprising the following steps: simulating an actual casting process to prepare an eccentric hollow cylindrical casting, measuring and counting the total length L of surface cracks of the casting after the casting is poured, representing the coefficient of thermal cracking tendency of the alloy by utilizing the product C of the total length L of the surface cracks of the eccentric hollow cylindrical casting and the wall thickness ratio R, wherein the larger the value C is, the larger the thermal cracking tendency of the alloy is represented, and vice versa, wherein:

wall thickness ratio

The coefficient of thermal cracking tendency C ═ lxr;

the eccentric hollow cylinder is of a cylindrical structure with a circular through hole in the axial direction, the diameter of the outer circle of the cross section of the eccentric hollow cylinder is phi 1, the diameter of the inner hole is phi 2, and the distance between the circle center of the outer circle and the circle center of the inner hole is the eccentricity m.

As a preferred technical scheme:

the height H of the eccentric hollow cylinder is 10-100 mm, the diameter phi 1 of the outer circle is 10-50 mm, the size range of the diameter phi 2 of the inner hole is (0.5-0.8) phi 1, the size range of the eccentricity m is (0.04-0.1) phi 1, and when m is equal to 0.1 phi 1, the phi 2 can not be 0.8 phi 1.

An eccentric hollow cylindrical casting is prepared by adopting a sand mold process.

The pouring temperature for casting the eccentric hollow cylindrical casting is 620-700 ℃.

When different alloy hot cracking tendencies are compared, the eccentric hollow cylindrical casting adopts the same height, the same excircle diameter, the same inner hole diameter and the same eccentricity for accurate comparison.

The cast magnesium alloy is one of Mg-Zn system, Mg-Al system, Mg-Ca system, Mg-Zn-Zr system, Mg-Zn-Y system, Mg-Al-Ca system and Mg-Gd-Y system.

Drawings

FIG. 1 is a schematic view (cross section) of the structure of an eccentric hollow cylinder.

FIG. 2 is a schematic view (longitudinal section) of the eccentric hollow cylinder structure.

Detailed Description

The eccentric hollow cylinder structure that this application embodiment adopted is shown in fig. 1, 2, eccentric hollow cylinder is the cylindrical structure that the axial has circular through-hole, and its cross section excircle diameter is Φ 1, and the hole diameter is Φ 2, and the distance between excircle centre of a circle O1 and the hole centre of a circle O2 is eccentricity m, and eccentric hollow cylinder height is H.

Example 1

Evaluation of heat cracking tendency of cast magnesium alloy AZ 91:

simulating an actual casting process to prepare an eccentric hollow cylinder casting, wherein the height H of the eccentric hollow cylinder is 50 mm, the diameter phi 1 of the outer circle of the cross section is 20 mm, the diameter phi 2 is 14.5 mm, and the eccentricity m is 1.5 mm; the casting temperature of the cast magnesium alloy is 620-700 ℃; the eccentric hollow cylindrical casting is prepared by adopting a sand mold process;

the total length L of cracks on the surface of the eccentric hollow cylindrical casting is 0.56 mm, the wall thickness ratio R is 3.4, and the coefficient of hot cracking tendency C is L multiplied by R is 1.904.

Example 2

Evaluation of the tendency of the cast magnesium alloy to heat cracking EW 75:

simulating an actual casting process to prepare an eccentric hollow cylinder casting, wherein the height H of the eccentric hollow cylinder is 60 mm, the diameter phi 1 of the outer circle of the cross section is 30 mm, the diameter phi 2 is 20 mm, and the eccentricity m is 1.5 mm; the casting temperature of the cast magnesium alloy is 620-700 ℃; the eccentric hollow cylindrical casting is prepared by adopting a sand mold process;

the total length L of cracks on the surface of the eccentric hollow cylindrical casting is 1.148 mm, the wall thickness ratio R is 1.857, and the coefficient of hot cracking tendency C is L multiplied by R is 2.132.

Example 3

Evaluating the heat cracking tendency of the cast magnesium alloy ZK 60:

simulating an actual casting process to prepare an eccentric hollow cylinder casting, wherein the height H of the eccentric hollow cylinder is 90 mm, the diameter phi 1 of the outer circle of the cross section is 45 mm, the diameter phi 2 is 26 mm, and the eccentricity m is 2.5 mm; the casting temperature of the cast magnesium alloy is 620-700 ℃; the eccentric hollow cylindrical casting is prepared by adopting a sand mold process;

the total length L of cracks on the surface of the eccentric hollow cylindrical casting is 1.49 mm, the wall thickness ratio R is 1.714, and the coefficient of hot cracking tendency C is L multiplied by R is 2.55.

Example 4

Evaluation of cast magnesium alloy MgZn_4.5Y₆Tendency to heat cracking:

simulating an actual casting process to prepare an eccentric hollow cylinder casting, wherein the height H of the eccentric hollow cylinder is 15 mm, the diameter phi 1 of the outer circle of the cross section is 10 mm, the diameter phi 2 is 6 mm, and the eccentricity m is 0.8 mm; the casting temperature of the cast magnesium alloy is 620-700 ℃; the eccentric hollow cylindrical casting is prepared by adopting a sand mold process;

the total length L of cracks on the surface of the eccentric hollow cylindrical casting is 1.42 mm, the wall thickness ratio R is 2.33, and the coefficient of hot cracking tendency C is L multiplied by R is 3.31

The invention is not the best known technology.

The above embodiments are merely illustrative of the technical ideas and features of the present invention, and the purpose thereof is to enable those skilled in the art to understand the contents of the present invention and implement the present invention, and not to limit the protection scope of the present invention. All equivalent changes and modifications made according to the spirit of the present invention should be covered within the protection scope of the present invention.