Rolling and preparation method of magnesium alloy sheet

Abstract

The present disclosure provides a high-efficient rolling process for magnesium alloy sheet. Parameters of the rolling process are: the rolling speed of each rolling pass is 10-50 m/min, the rolling reduction of each rolling pass is controlled to be 40-90%, and both the preheating temperature before rolling and the rolling temperature of each rolling pass are 250-450° C. The present disclosure also provides a preparation method for magnesium alloy sheet, comprising: 1) preparing rolling billets; 2) high-efficient hot rolling; and 3) performing annealing. The rolling process can improve the mechanical performance especially, the strength and ductility of the sheet.

Claims

1. A rolling process for magnesium alloy sheets, wherein billets are rolled in a rough rolling step and a high-efficiency hot rolling step, and wherein, in the rough rolling step, a reduction of each pass is 10-30%, and a rolling speed of each pass is 10 m/min to 45 m/min, and in the high-efficiency hot rolling step, a rolling speed in each rolling pass is 10-50 m/min, rolling reduction in each rolling pass is 40-90%, the billets are preheated 1-15 min before rolling in each rolling pass, and the temperature of the preheating before rolling and a temperature of rolling in each rolling pass are controlled to be 250-450° C.

2. A method for producing magnesium alloy sheets, comprising the following steps of: 1) preparing rolled magnesium alloy billets by a rough rolling, wherein a reduction of each pass is controlled to be 10-30% and a rolling speed of each pass is controlled to be 10 m/min to 45 m/min, 2) effectively hot-rolling the rolled magnesium alloy billets to at least a target level, wherein rolling speed in each rolling pass is 10-50 m/min, rolling reduction in each rolling pass is controlled to be 40-90%, and the rolled magnesium alloy billets are preheated 1-15 min before rolling in each rolling pass, and a temperature of the preheating before rolling and a temperature of rolling in each rolling pass are controlled to be 250-450° C., and 3) annealing at an annealing temperature of 150-400° C. and annealing time of 10-300 s.

3. The method according to claim 2, wherein in the step 1), the step of preparing the rolled magnesium alloy billets comprises smelting and casting an ingot, homogenization treatment, sawing the ingot and rough rolling the ingot.

4. The method according to claim 3, wherein in the step 1), the rolled magnesium alloy billets are preheated before each pass of rough rolling, and preheating temperature and rolling temperature in each pass of rough rolling are controlled to be 250-450° C.

5. The method according to claim 2, wherein in the step 1), the step of preparing the rolled magnesium alloy billets is prepared by a twin-roll casting method.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a micrograph after the annealing step of Comparative Example B1.

(2) FIG. 2 is a micrograph after the annealing step of Comparative Example B2.

(3) FIG. 3 is a micrograph after the annealing step of Example A1.

(4) FIG. 4 is a graph showing the relationship between the reduction and the tensile curve at room temperature of Example A1, Comparative Example B1, and Comparative Example B2.

(5) FIG. 5 is a micrograph after the annealing step of Comparative Example B3.

(6) FIG. 6 is a micrograph after the annealing step of Comparative Example B4.

(7) FIG. 7 is a micrograph after the annealing step of Example A2.

(8) FIG. 8 is a graph showing the relationship between the reduction and the tensile curve at room temperature of Example A2, Comparative Example B3, and Comparative Example B4.

(9) FIG. 9 is a micrograph after the annealing step of Comparative Example B5.

(10) FIG. 10 is a micrograph after the annealing step of Comparative Example B6.

(11) FIG. 11 is a micrograph after the annealing step of Example A3.

(12) FIG. 12 is a graph showing the relationship between the reduction and the tensile curve at room temperature of Example A3, Comparative Example B5, and Comparative Example B6.

DETAILED DESCRIPTION

(13) The following further describes and illustrates the high-efficiency rolling process for high-strength and high-ductility magnesium alloy sheets and the preparation method for high-strength and high-ductility magnesium alloy sheets according to the present invention with reference to the drawings and specific Examples, whereas the explanation and demonstration do not improperly limit the technical solutions of the present invention.

EXAMPLES A1-A6 AND COMPARATIVE EXAMPLES B1-B9

(14) The above Examples A1˜A6 are obtained by the preparation method for high-strength and high-ductility magnesium alloy sheets of the present invention, which includes the following steps:

(15) (1) Preparing rolling billets:

(16) wherein, the preparation process of the rolling billets in Examples A1˜A2, A4, A5 is as follows:

(17) (1a) melting: the raw materials were placed in a steel crucible and mixed; the crucible and raw materials were then placed in an induction furnace and heated to 760° C. for melting; during the melting process, argon gas was injected into the induction furnace as a protective atmosphere to prevent combustion;

(18) (1b) casting ingot: after the melting, the molten magnesium alloy liquid was casted in a preheated steel mold at 200° C.; the ingot size is 55 mm (length)*30 mm (width)*120 mm (height);

(19) (1c) homogenization treatment: homogenizing at 300° C. for 12 hr, and then homogenizing at 430° C. for 4 hr;

(20) (1d) sawing ingot: after homogenization, the ingots were sawn into slabs with a thickness of 5 mm according to thickness requirements;

(21) (1e) rough rolling: parameters of the rolling process were as follows: the roll diameter was 75 mm, the rolling speed of each pass was 10˜50 m/min, the reduction of each pass was 10˜30%, the billets were preheated before rolling in each rolling pass, the preheating temperature before rolling and the rolling temperature were 250˜450° C., and the heat preservation time of preheating was 1˜15 min.

(22) By rolling the billets of Examples A3 and A6 with twin rollers, an AZ31 alloy billet with an initial thickness of 2 mm was obtained.

(23) (2) High-efficiency hot rolling: the roll diameter was 75 mm, the rolling speed of each pass was 10˜50 m/min, the reduction of each pass was 40˜90%, the billets were preheated before rolling in each rolling pass, the preheating temperature before rolling and the rolling temperature were 250˜450° C., and the heat preservation time of preheating was 1˜15 min.

(24) (3) Annealing: the annealing temperature was 150˜400° C. and the annealing time was 10˜300 s.

(25) It should be noted that the rolling billets of Comparative Examples B5, B6 and B9 were also prepared by twin-roll casting, while Comparative Examples B1˜B4, B7, B8 were obtained by steps of melting, casting ingot, homogenization treatment, sawing ingot and rough rolling.

(26) Table 1 shows specific process parameters of Examples A1˜A6 and Comparative Examples B1˜B9.

(27) TABLE-US-00001 TABLE 1 Step (1) Step (2) Rough rolling Rough rolling Preheating Total pass High-efficient Example Alloy composition Rough rolling single-pass temperature time before in rough hot rolling number* and conditions speed (m/min) reduction (%) (° C.) rolling (min) rolling speed (m/min) A1 Mg—3Al—1Zn—0.3Mn cast 15 20 400 6 4 15 magnesium alloy A2 Mg—1Zn—0.2Nd—0.2Zr cast 45 30 400 6 3 15 magnesium alloy A3 Mg—3Al—1Zn—0.3Mn twin- — — — — — 15 roll cast magnesium alloy A4 Mg—3Al—1Zn—0.3Mn cast 50 20 450 1 4 40 magnesium alloy A5 Mg—1Zn—0.2Nd—0.2Zr cast 10 10/20/30 260 15  3 10 magnesium alloy A6 Mg—3Al—1Zn—0.3Mn twin- — — — — — 50 roll cast magnesium alloy Step (2) Step (3) High-efficiency Rolling Preheating Total pass of Annealing Example hot rolling single- temperature time before high-efficient temperature Annealing number* pass reduction (%) (° C.) rolling (min) hot rolling (° C.) time (s) A1 50 400 6 1 200 60 A2 50 400 6 1 300 60 A3 50 400 1 1 200 60 A4 90 450 1 1 150 300 A5 43 260 15 1 400 10 A6 80 420 5 1 200 280 Step (1) Comparative Hot rolling Rolling Preheating Total pass Step (2) Example Alloy composition Hot rolling single-pass temperature time before in hot Hot rolling number and conditions speed (m/min) reduction (%) (° C.) rolling (min) rolling speed (m/min) B1 Mg—3Al—1Zn—0.3Mn cast 15 20 400 6 4 15 magnesium alloy B2 Mg—3Al—1Zn—0.3Mn cast 15 20 400 6 3 15 magnesium alloy B3 Mg—1Zn—0.2Nd—0.2Zr cast 45 30 400 6 3 15 magnesium alloy B4 Mg—1Zn—0.2Nd—0.2Zr 45 30 400 6 3 15 magnesium alloy B5 Mg—3Al—1Zn—0.3Mn twin- — — — — — 15 roll cast magnesium alloy B6 Mg—3Al—1Zn—0.3Mn twin- — — — — — 15 roll cast magnesium alloy B7 Mg—3Al—1Zn—0.3Mn cast  2 20 450 1 4 2 magnesium alloy B8 Mg—1Zn—0.2Nd—0.2Zr cast  2 10/20/20/20 300 15  4 2 magnesium alloy B9 Mg—3Al—1Zn—0.3Mn twin- — — — — — 2 roll cast magnesium alloy Step (2) Step (3) Comparative Hot rolling Rolling Preheating Annealing Example single-pass temperature time before Total pass of temperature Annealing number reduction (%) (° C.) rolling (min) hot rolling (° C.) time (s) B1 10 400 6 1 200 60 B2 30 400 6 1 200 60 B3 10 400 6 1 300 60 B4 30 400 6 1 300 60 B5 10 400 1 1 200 60 B6 30 400 1 1 200 60 B7 30 450 1 3 200 1800 B8 30 300 15 1 400 1800 B9 20 400 5 3 350 1800 *Note: For the multi-pass rolling in the table, if there is only one value for single-pass reduction, it means that the reductions in each pass are the same.

(28) Magnesium alloy sheets of Examples A1˜A6 and Comparative Examples B1˜B9 were sampled and the middle portion of the samples were taken to observe the microstructures of the sheet. The microstructures of the sheets are shown in the following figures. The relevant mechanical properties were determined by conventional tensile test methods; wherein the tensile strain rate was 10.sup.−3/s and the gauge length was 10 mm. The results obtained after the tests are shown in Table 2.

(29) Table 2 shows the parameters of mechanical properties of Examples A1˜A6 and Comparative Examples B1˜B9.

(30) TABLE-US-00002 TABLE 2 Yield Tensile Uniform Elongation Number* strength (MPa) strength (MPa) elongation (%) (%) A1 243 300 13 24 A2 244 265 8 29 A3 263 304 10 20 A4 245 308 20 26 A5 234 255 16 31 A6 265 318 15 24 B1 221 270 9 15 B2 235 280 11 20 B3 215 236 7 14 B4 238 259 7 18 B5 255 291 8 16 B6 261 303 8 13 B7 119 230 15 23 B8 141 212 9 30 B9 195 264 12 22

(31) As can be seen from Table 2, all yield strengths of Examples A1˜A6 are 234 MPa or more and all tensile strengths of Examples A1˜A6 are 255 MPa or more, which indicates that the magnesium alloy sheets of Examples have relatively high strengths; the uniform elongations of Examples A1˜A6 are 8% or more and the elongations of Examples A1˜A6 are 20% or more, which indicates that the magnesium alloy sheets of Examples have high ductility and good plasticity. The yield strength, tensile strength, uniform elongation and elongation of Examples A1˜A6 are all higher than the yield strength, tensile strength, uniform elongation and elongation of the corresponding Comparative Examples. In particular, the yield strengths of the magnesium alloy sheets of Examples are greatly improved. For example, compared with the yield strength of Comparative Example B9 (195 MPa), the yield strength of Example A6 (265 MPa) increased by 35.9%; compared with the yield strength of Comparative Example B8 (141 MPa), the increase in the yield strength of Example A5 (234 MPa) reached about 66%; compared with the yield strength of the comparative example B7 (119 MPa), the yield strength of the example A4 (245 MPa) even increased by about 106%.

(32) FIGS. 1, 2 and 3 show the microstructure after the annealing step of Comparative Example B1, Comparative Example B2 and Example A1, respectively.

(33) As shown in FIG. 1, if necessary, refer to Table 1: the single-pass reduction in Comparative Example B1 is 10%; the deformation of the magnesium alloy sheet is small due to the small reduction, thus making the recrystallization of the sheet incomplete. The fraction of recrystallized grains is only 22%, and the grains are coarse, the average grain size is about 9 μm.

(34) As shown in FIG. 2, if necessary, refer to Table 1: the single-pass reduction in Comparative Example B2 is 30%, which is larger than that of Comparative Example B1, resulting in a relatively large deformation of the magnesium alloy sheet; although the recrystallization of the magnesium alloy sheet of Comparative Example B2 is still incomplete, the fraction of recrystallized grains thereof is about 40%, higher than that of Comparative Example B1, and the average grain size thereof is smaller, about 6 μm.

(35) As shown in FIG. 3, if necessary, refer to Table 1: the single-pass reduction in Example A1 is 50%, which is larger than that of Comparative Examples B1 and B2. The deformation of the magnesium alloy sheet is larger, the grain structure of the magnesium alloy sheet is clearly refined, and the large-size deformed grains are greatly reduced. Compared with the grain sizes of the magnesium alloy sheets of Comparative Examples B1 and B2 shown in FIGS. 1 and 2, the grain size of Examples A1 shown in FIG. 3 is smaller and the grain size thereof is more uniform. The average grain size is about 4 μm and the fraction of recrystallized grains reaches about 68%.

(36) As shown in FIGS. 1 and 2 and in combination with the contents shown in Table 1, since Comparative Examples B1 and B2 use relatively low single-pass reductions, the recrystallized grain sizes are relatively large and the effects of recrystallization on grain refinement are not obvious in the microstructures after the annealing step of Comparative Examples B1 and B2. As shown in FIG. 3 and in combination with the contents shown in Table 1, since Example A1 uses a relatively high single-pass reduction, the degree of recrystallization is high, the grain size is small and the grain size is uniform in the microstructure of Example A1.

(37) FIG. 4 shows the relationship between the single-pass reduction and the tensile curve at room temperature of Example A1, Comparative Example B1 and Comparative Example B2.

(38) As shown in FIG. 4 and in combination with Tables 1 and 2, the single-pass reduction in Comparative Example B1 is 10%, the single-pass reduction in Comparative Example B2 is 30%, while the single-pass reduction in Example A1 is 50%; the mechanical properties of the magnesium alloy sheet increase with the increase of the single-pass reduction. Specifically, the yield strength, tensile strength, uniform elongation and elongation of Example A1 are all higher than the yield strength, tensile strength, uniform elongation and elongation of Comparative Examples B1 and B2.

(39) FIGS. 5, 6 and 7 show the microstructures after the annealing step of Comparative Example B3, Comparative Example B4 and Example A2, respectively.

(40) As shown in FIG. 5, if necessary, refer to Table 1: the single-pass reduction in Comparative Example B3 is 10%; the deformation of the magnesium alloy sheet is small due to the small reduction, thus making the recrystallization of the sheet incomplete. The fraction of recrystallized grains is only 30%, and as shown in FIG. 5, the grains are coarse, and the average grain size is about 7 μm.

(41) As shown in FIG. 6, if necessary, refer to Table 1: the single-pass reduction in Comparative Example B4 is 30%, which is larger than that of Comparative Example B3, resulting in a relatively large deformation of the magnesium alloy sheet; although the recrystallization of the magnesium alloy sheet of is still incomplete, the fraction of recrystallized grains thereof is about 48%, higher than that of Comparative Example B3 and the average grain size thereof is smaller, about 4 μm.

(42) As shown in FIG. 7, if necessary, refer to Table 1: the single-pass reduction in Example A2 is 50%, which is larger than that of Comparative Examples B3 and B4. The deformation of the magnesium alloy sheet is larger, the grain structure of the magnesium alloy sheet is clearly refined, and the large-size deformed grains are greatly reduced. Compared with the grain sizes of the magnesium alloy sheets of Comparative Examples B3 and B4 shown in FIGS. 5 and 6, the grain size of Examples A2 shown in FIG. 7 is smaller and the grain size thereof is more uniform. The average grain size is about 3 μm and the fraction of recrystallized grains reaches about 66%.

(43) As shown in FIGS. 5 and 6 and in combination with the contents shown in Table 1, since Comparative Examples B3 and B4 use relatively low single-pass reductions, the recrystallized grain sizes are relatively large and the effects of recrystallization on grain refinement are not obvious in the microstructures after the annealing step of Comparative Examples B3 and B4. As shown in FIG. 7 and in combination with the contents shown in Table 1, since Example A2 uses a relatively high single-pass reduction, the effect of recrystallization is obvious, the grain size is small and the grain size is uniform in the microstructure of Example A2.

(44) FIG. 8 shows the relationship between the single-pass reduction and the tensile curve at room temperature of Example A2, Comparative Example B3 and Comparative Example B4.

(45) As shown in FIG. 8 and in combination with Tables 1 and 2, the single-pass reduction in Comparative Example B3 is 10%, the single-pass reduction in Comparative Example B4 is 30%, while the single-pass reduction in Example A2 is 50%; the stress and strain index of the magnesium alloy sheet increase with the increase of the single-pass reduction. Specifically, the yield strength, tensile strength, uniform elongation and elongation of Example A2 are all higher than the yield strength, tensile strength, uniform elongation and elongation of Comparative Examples B3 and B4.

(46) FIGS. 9, 10 and 11 show the microstructures after the annealing step of Comparative Example B5, Comparative Example B6 and Example A3, respectively.

(47) As shown in FIG. 9, if necessary, refer to Table 1: the single-pass reduction in Comparative Example B5 is 10%; the deformation of the magnesium alloy sheet is small due to the small reduction, thus making the recrystallization of the sheet incomplete. The fraction of recrystallized grains is only 28%, the grains are coarse as shown in FIG. 9 and the average grain size is about 12 μm.

(48) As shown in FIG. 10, if necessary, refer to Table 1: the single-pass reduction in Comparative Example B6 is 30%, which is larger than that of Comparative Example B5, resulting in a relatively large deformation of the magnesium alloy sheet; although the recrystallization of the magnesium alloy sheet is still incomplete, the fraction of recrystallized grains thereof is about 48%, higher than that of Comparative Example B5 and the average grain size thereof is smaller, about 7 μm.

(49) As shown in FIG. 11, if necessary, refer to Table 1: the single-pass reduction in Example A3 is 50%, which is larger than that of Comparative Examples B5 and B6. The deformation of the magnesium alloy sheet is larger, the grain structure of the magnesium alloy sheet is clearly refined, and the large-size deformed grains are greatly reduced. Compared with the grain sizes of the magnesium alloy sheets of Comparative Examples B5 and B6 shown in FIGS. 9 and 10, the grain size of Examples A3 shown in FIG. 11 is smaller and the grain size thereof is more uniform. The average grain size is about 4 μm and the fraction of recrystallized grains reaches about 67%.

(50) As shown in FIGS. 9 and 10 and in combination with the contents shown in Table 1, since Comparative Examples B5 and B6 use relatively low single-pass reductions, the recrystallized grain sizes are relatively large and the effects of recrystallization on grain refinement are not obvious in the microstructures after the annealing step of Comparative Examples B5 and B6. As shown in FIG. 11 and in combination with the contents shown in Table 1, since Example A3 uses a relatively high single-pass reduction, the effect of recrystallization is obvious, the grain size is small and the grain size is uniform in the microstructure of Example A3.

(51) FIG. 12 shows the relationship between the single-pass reduction and the tensile curve at room temperature of Example A3, Comparative Example B5 and Comparative Example B6.

(52) As shown in FIG. 12 and in combination with Tables 1 and 2, the single-pass reduction in Comparative Example B5 is 10%, the single-pass reduction in Comparative Example B6 is 30%, while the single-pass reduction in Example A3 is 50%; the stress and strain index of the magnesium alloy sheet increase with the increase of the single-pass reduction. Specifically, the yield strength, tensile strength, uniform elongation and elongation of Example A3 are all higher than the yield strength, tensile strength, uniform elongation and elongation of Comparative Examples B5 and B6.

(53) It should be noted that the above is only specific Examples of present invention. It is obvious that present invention is not limited to the above Examples, and there are many similar changes. All variations that a person skilled in the art derives or associates directly from the disclosure of present invention shall fall within the protection scope of present invention.