JP2018513914A - Formable magnesium-type wrought alloy - Google Patents

Abstract

(Wt%): 0.1 to 2.0 Zn; 0.05 to 1.5 Ca; 0.1 to 1.0 Zr; 0 to 1.3 rare earth element containing Gd or Y or Its mixture; 0-0.3 Sr, Al: 0-0.7; Magnesium-type extension alloy consisting essentially of the balance Mg and other inevitable impurities. [Selection] Figure 2

Description

Detailed Description of the Invention

[Technical field]
[1] The present invention generally relates to a novel magnesium-calcium alloy composition. More particularly, the present invention relates to magnesium-zinc-rare earth-calcium-zirconium and magnesium-calcium-zinc- (zirconium) type wrought alloys containing several alloying elements to enhance formability. In particular, the present invention relates to a magnesium type wrought alloy sheet formed therefrom and a method or process for forming the magnesium type wrought alloy sheet.

[Background of the invention]
[2] The following discussion of the background of the present invention is intended to facilitate understanding of the present invention. However, it is understood that this discussion is neither an admission nor an admission that any material mentioned is known or part of the common general knowledge published at the priority date of the application. .

[3] Magnesium (Mg) is the lightest structural material having a density of 1.74 g / cm ³ at 20 ° C., the density being about 2/3 of the density of aluminum (Al) and 1 / of the density of steel. 4. This property makes magnesium a promising candidate for replacing steel and Al alloys. There is a growing interest in developing magnesium sheet alloys for structural applications, especially in the automotive, aerospace, light rail, and high-speed train industries. This is because the broad application of magnesium alloys can help save energy and thereby reduce running costs. However, conventional Mg sheet alloys such as AZ31 and ZK60 have not been widely used in the industrial field due to their poor ductility and formability at medium temperatures.

  [4] Conventional magnesium stretch / sheet alloys, such as AZ31, ZK60, develop strong bottom texture during the thermomechanical process and have strong mechanical anisotropy. Therefore, these alloys are less formable than competing metals such as aluminum and steel alloys at medium temperatures. The limited formability of existing commercial magnesium alloys at moderate temperatures limits the wide application of these materials.

  [5] The formability of the Mg alloy sheet can be improved by modifying the alloy composition and controlling the processing parameters. The Mg-RE (rare earth) alloy sheet exhibits a substantial improvement in ductility and formability compared to the commercially available AZ31 alloy sheet. Furthermore, according to literature reported in recent years, when a non-RE element, that is, Zn is added to the Mg-RE alloy, it is possible to impart ductility and formability superior to those of the Mg-RE binary alloy sheet. However, there is currently no literature reporting a method for producing a magnesium alloy sheet having better ductility and formability than Mg-Zn-Gd alloy sheets.

  [6] Therefore, it is desirable to develop a novel magnesium alloy, preferably an Mg type wrought alloy containing Ca, for forming sheets with excellent formability and mechanical properties.

[Summary of Invention]
[7] A first aspect of the present invention is (wt%): 0.1 to 2.0 Zn, 0.05 to 1.5 Ca, 0.1 to 1.0 Zr, 0 to 1 .3, a rare earth element containing Gd or Y, or a mixture thereof, 0-0.3 Sr, Al: 0-0.7 wt%, the balance Mg and other inevitable impurities, and a magnesium type extension consisting essentially of Provide alloys.

  [8] The present invention provides, in this first aspect, magnesium-zinc-rare earth-calcium-zirconium and magnesium-calcium-zinc- (zirconium) types that include several alloying elements to enhance formability. It is related with the alloy for extending. The alloy includes a dilute alloying composition wherein the total amount of alloying elements is preferably less than (or equal to) 4 wt%. Without being limited to any one theory, the inventors have developed a dilute alloy comprising the addition of the low-cost alloying element Ca to Mg-Zn-RE-Zr and Mg-Zn- (Zr) alloys. It has been found that the chemical composition can significantly weaken the texture and improve the formability of the alloy. The formability of the obtained Mg—Zn—RE—Ca—Zr alloy having an appropriate composition is superior to that of the existing Mg—Zn—Gd— (Zr) alloy.

[9] Depending on the alloy composition, a certain amount of rare earth element may be present. In the most common form, the magnesium alloy comprises (wt%): 0 to 1.3 rare earth elements or mixtures thereof, but in some forms the rare earth elements or mixtures thereof are 0.05 wt% and 1 .3 wt% may be included. The rare earth element or mixture thereof may comprise a lanthanide series or yttrium rare earth element. For the purposes of this specification, lanthanide elements include a group of elements having atomic numbers included in increments from 57 (lanthanum) to 71 (lutetium). Such elements are called lanthanides because the lighter elements in the series are chemically similar to lanthanum. Strictly speaking, lanthanum is a group 3 element, and the ion La ³⁺ does not have f electrons. However, for the purposes of this specification, it will be understood that lanthanum is included as one of the lanthanide series rare earth elements. For the purposes of the present invention, yttrium will also be encompassed by the term “rare earth element”. Accordingly, the lanthanide series rare earth elements include lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium and lutetium. In some embodiments, the rare earth component comprises gadolinium (Gd). In other embodiments, the rare earth component comprises a mixture of gadolinium (Gd) and lanthanum (La). In other embodiments, the rare earth component comprises a mixture of gadolinium and yttrium. In other embodiments, the rare earth component comprises gadolinium or a mixture of yttrium and lanthanide series rare earth elements. An advantage of embodiments comprising the lanthanide series or yttrium rare earth elements is their relatively high solubility in magnesium.

  [10] Alloying elements are understood to function as follows: Rare earth elements are added to weaken the texture and improve the formability of Mg-Zn alloys at medium temperatures. Zirconium is added as a grain refiner. Aluminum is added to promote the age hardening response of Mg-Ca-Zn- (Zr) type alloys.

  [11] A second aspect of the present invention is (wt%): Zn: 0.1 to 2.0, Ca: 0.05 to 1.5, Zr: 0.1 to 1.0, Gd: 0 ~ 1.0, preferably 0.05 to 1.0, Sr: 0 to 0.3, La: 0 to 0.3, Al: 0 to 0.7, and the remaining Mg and other unavoidable impurities. A magnesium-type wrought alloy is provided, wherein the total weight percent of alloying elements is less than 4%.

  [12] In a preferred embodiment, the magnesium type spreading alloy is (wt%): Ca: 0.3-1.0, Zn: 0.3-1.0, Zr: 0.2-0. 7, essentially consisting of Gd: 0.1 to 0.5, Sr: 0 to 0.2, La: 0 to 0.2, Al: 0 to 0.5, and the balance Mg and other inevitable impurities. Here, the total weight% of alloying elements is less than 4%.

[13] In some embodiments, the present invention is classified into two common calcium-containing magnesium extending alloy compositions that include several alloying elements to enhance the formability of the alloy composition. can do. Common alloy groups are as follows.
Group 1: Mg-Zn-Gd-Ca-Zr type alloys; and Group 2: Mg-Ca-Zn- (Zr) type alloys

  [14] The specific alloy compositions of these individual groups will now be discussed.

Group 1: Mg-Zn-Gd-Ca-Zr type alloys.
[15] In Group 1, the Mg alloy comprises more than 0.5% but less than 2.0% Zn, 0.05% to 1.0% Gd, 0.05% to 1.0% Ca, 0.1% -1.0% Zr, 0% -0.3% strontium (Sr), 0% -0.3% lanthanum (La), 0% -0.7% Al and the balance Contains Mg and other inevitable impurities. In addition, preferably the amount of Zn ranges from 0.5% to 1.5%. Furthermore, the amount of Gd is preferably more than 0.1% and less than 0.5%. In addition, it is preferable to contain more than 0.1% and less than 0.7% Ca. Furthermore, the amount of Zr is preferably more than 0.2% and less than 0.7%. In addition, the amount of Sr is preferably less than 0.2%. Furthermore, the content of La is preferably less than 0.2%. In addition, the amount of Al is preferably more than 0.2% and less than 0.5%.

Group 2: Mg-Ca-Zn- (Zr) type alloys.
[16] In Group 2, the Mg alloy contains more than 0.3% but less than 1.5% Ca, 0.1% to 0.8% Zn, 0% to 1.0%, preferably 0.8%. 1% to 1.0% Gd, 0% to 0.7% Al, 0% to 0.3% Sr, 0.1% to 1.0% Zr, and the balance Mg, and other inevitable Contains impurities. In addition, the Ca content is preferably in the range of 0.6% to 1.0%. Furthermore, the amount of Zn is preferably more than 0.3% and less than 0.5%. In addition, the amount of Gd is preferably greater than 0.1% and less than 0.5%. Further, the amount of Al is preferably more than 0.1% and less than 0.7%, more preferably the amount of Al is more than 0.2% and less than 0.5%. In addition, the amount of Sr is preferably less than 0.2%. Furthermore, the amount of Zr is preferably more than 0.2% and less than 0.7%.

  [17] The total amount of alloying elements is preferably less than 4%, more preferably less than 3%, and even more preferably less than 2.5%. Further alloying additives cause the formation of second phase particles that can act as nucleation sites for cracking during deformation, thus reducing the formability of Mg-stretching alloys. It is understood that it may be harmful.

  [18] In an embodiment, the magnesium type extension alloy includes Mg-1Zn-0.4Gd-0.5Zr, Mg-1Zn-0.4Gd-0.2Ca-0.5Zr, Mg-1Zn-0. 4Gd-0.5Ca-0.5Zr, Mg-1Zn-0.4Gd-0.2Ca-0.1Sr-0.5Zr, Mg-1Zn-0.4Gd-0.2Ca-0.1La-0.5Zr, Mg-0.8Ca-0.4Zn, Mg-0.8Ca-0.4Zn-0.4Gd, Mg-0.8Ca-0.4Zn-0.3Al, Mg-0.8Ca-0.4Zn-0. 3Al-0.1Sr, Mg-0.8Ca-0.4Zn-0.5Zr, Mg-0.8Ca-0.4Zn-0.1Sr-0.5Zr, Mg-0.8Ca-0.4Zn-0. 4Gd-0.5Zr, or Mg-0.8Ca-0.4Zn-0 Selected from one of 1Sr-0.4Gd-0.5Zr.

  [19] In a preferred embodiment, the magnesium type spreading alloy is Mg-1Zn-0.4Gd-0.2Ca-0.5Zr, or Mg-0.8Ca-0.4Zn-0.1Sr-0. It is selected from one of 4Gd-0.5Zr.

  [20] Manganese (Mn) can also be added to both Zr-free and Zr-containing alloys to minimize iron content and further improve corrosion resistance. When present, the amount of Mn is preferably more than 0.05% and less than 0.7%, more preferably more than 0.1% and less than 0.5%.

  [21] Magnesium type alloys preferably contain a minimal amount of incidental impurities. In some embodiments, the magnesium-type alloy includes less than 0.5 wt% incidental impurities, more preferably less than 0.2 wt%. Incidental impurities include Li, Be, Ca, Sr, Ba, Sc, Ti, Hf, Mn, Fe, Cu, Ag, Ni, Cd, Al, Si, Ge, Sn, and Th alone or in combination. Can be included in various amounts.

  [22] The present invention also relates to a magnesium type wrought alloy sheet comprising at least one magnesium type wrought alloy according to the first or second aspect of the present invention. In this regard, the present inventors are not aware of the application of the Mg—Ca—Zn— (Zr) alloy system sheet form in the reported literature or patent publications. Therefore, the present inventors consider that the sheet form of the magnesium type wrought alloy is unique.

[23] The present invention also relates to a method of making a magnesium-type alloy sheet product. Accordingly, a third aspect of the present invention is a method of manufacturing a magnesium type alloy sheet product comprising:
Providing a magnesium alloy melt from a magnesium type alloy according to the first or second aspect of the invention;
Casting the magnesium alloy melt into a slab or strip according to a predetermined thickness;
Homogenizing or preheating the cast slab or strip;
Subsequently, in order to reduce the thickness of the homogenized slab or strip, the homogenized or preheated slab or strip is hot-rolled at an appropriate temperature to produce an alloy sheet product of a predetermined thickness. And steps to
Annealing the alloy sheet product for a time at an appropriate temperature;
Providing a method.

  [24] The magnesium alloy melt can be produced using any suitable method. In many embodiments, the individual elements were mixed and melted in a furnace, such as a high frequency induction melting furnace, in a suitable vessel such as a mild steel crucible to a temperature above the liquidus temperature for this alloy embodiment. In some embodiments, the melt is heated to about 760 ° C. under an argon atmosphere.

  [25] The casting step can include any suitable casting process. For example, the casting step may include casting an ingot or billet. In other embodiments, the casting step may include casting into a sheet or strip. In some embodiments, casting includes casting the magnesium alloy melt directly into one of a chill (DC) caster, a sand mold caster, or a mold caster. For example, the casting step may include using a DC casting billet that is subsequently extruded after preheating to form a slab or strip. In other embodiments, the casting step includes feeding a magnesium alloy melt between the rolls of a twin roll caster to create a strip.

  [26] Homogenization or preheating of the cast slab or strip preferably occurs at a temperature between 300-500 ° C. The actual homogenization temperature depends on the alloy composition. In some embodiments, the cast slab or strip is homogenized or preheated followed by quenching, preferably water quenching. The homogenization or preheating of the cast slab or strip is preferably performed for about 0-24 hours.

  [27] The homogenized slab or strip is preferably machined into a 5 mm thick strip and then hot rolled. Hot rolling is preferably performed in a temperature range of 300 to 550 ° C, more preferably 350 to 500 ° C. Hot rolling typically results in a total thickness reduction of 50-95%, preferably 70-80%.

  [28] In some embodiments, hot rolling is performed using multiple rolling passes, wherein after each rolling pass, the sheet is at a temperature in the range of 350-500 ° C. before the next rolling. It is reheated with. The sheet is reheated for about 5-20 minutes, preferably 5-10 minutes. The thickness reduction per pass is preferably about 20%. Thus, the total thickness can be about 80% because the thickness reduction per pass is about 20%.

  [29] After final rolling, the sheet undergoes a final annealing treatment to remove the accumulated strain through static recrystallization. The annealing temperature is preferably ± 50 ° C. from the inflection point of the annealing curve obtained for a standard period of 1 hour for the alloy composition. Further, the period for annealing the alloy sheet product is preferably about 1 minute to 24 hours.

  [30] We have found that various embodiments of the magnesium-calcium-zinc- (zirconium) type alloys of the present invention can be strengthened by artificial aging treatment. Thus, in some embodiments, the method can further include subjecting the annealed alloy to an age hardening treatment comprising heating the alloy at 150 ° C. for at least 1 hour. The age hardening period depends on the time period necessary or sufficient to obtain maximum precipitation hardening.

  [31] The present invention will be described with reference to the accompanying drawings, which illustrate particularly preferred embodiments of the invention.

[32] FIG. 1 is a flow chart illustrating a method of making a magnesium wrought alloy according to the invention, including an experimental test regime. [33] FIG. 2 provides tensile stress-strain curves for as-annealed B1, B2, B3, B4, and B5 alloy sheets and comparative as-annealed AZ31 and T4-6016 Al alloy sheets. [34] FIG. 3 shows tensile stress of as-annealed B6, B7, B8, B9, B10, B11, B12, and B13 alloy sheets and comparative as-annealed AZ31 and T4-6016 Al alloy sheets. Provide strain curve. [35] FIG. 4 provides a plot of age hardening response of Mg—Ca—Zn— (Zr) type alloy sheets. [36] FIG. 5 provides a plot of the change in hardness of the B2 alloy sheet as a function of annealing time at temperatures of 350, 400, 450 and 500 ° C.

[Detailed description]
[37] The present invention relates to magnesium-zinc-rare earth-calcium-zirconium and magnesium-calcium-zinc- (zirconium) type wrought alloys containing several alloying elements to enhance formability. In the present invention, the formability of magnesium-zinc-rare earth-calcium-zirconium and magnesium-calcium-zinc- (zirconium) type extending alloys, such as Mg-Zn-Gd-Zr alloys, can be made into trace or dilute alloys. It is clarified that the addition of an amount of Ca improves.

  [38] FIG. 1 illustrates a flowchart illustrating a method of making a magnesium alloy sheet of the present invention. As shown in FIG. 1, magnesium-zinc-rare-earth-calcium-zirconium and magnesium-calcium-zinc- (zirconium) type wrought alloys according to the compositions described herein are first prepared in start step 105. Prepared.

  [39] Following the preparation of the melt, in step 110, the individual alloys are cast using a suitable casting technique. In some embodiments, the casting step may include casting an ingot, billet, bar, square or other shaped body. In other embodiments, the casting step may include casting into a sheet or strip.

  [40] Examples of casting techniques include twin roll casting (TRC), sand casting with or without a chill plate on two sides, casting or DC casting. It is understood that several direct chill (DC) casting methods and equipment suitable for magnesium alloys are known in the art and can be used in the process / method of the present invention. The strip or slab can also be made from a DC cast billet that is subsequently extruded again into the slab or strip using methods and equipment suitable for magnesium alloys known in the art.

  [41] In one embodiment, the alloy was melted and cast using a high frequency induction melting furnace with a mild steel crucible at about 760 ° C. under an argon atmosphere. The resulting melt was poured into an appropriately sized ingot 30 mm thick x 55 mm wide x 120 mm long.

  [42] Homogenization or preheating is used to reduce interdendritic segregation and compositional differences associated with the casting process. A suitable commercial practice is to select a temperature below the non-equilibrium solid phase, usually 5-10 ° C. Assuming that magnesium, calcium and zinc are the main components of the alloy, the temperature range is 300-500 ° C. depending on the alloy composition. The time required for the homogenization step depends on the size of the cast ingot, billet, strip or slab. A time of 2-4 hours is sufficient for TRC strips, while up to 24 hours are required for sand cast slabs or direct chill cast slabs. The homogenization process is followed by a quenching step, typically a water quenching step.

  [43] For experimental purposes, the homogenized ingot is machined into a 5 mm thick strip. However, it is understood that the strip can be formed using a number of other techniques, as discussed above in the casting step.

  [44] The homogenized ingot, strip or slab is then hot rolled at a suitable temperature in step 120. Depending on the casting material, different rolling steps may be used. The breakdown rolling step can be used for alloy slabs produced by sand casting, DC casting or any other type of casting and having a thickness greater than 25 mm. The purpose of this step is to refine and remove the cast structure in addition to reducing the thickness. The temperature of this step depends on the furnace available at the rolling facility, but temperatures between 350-500 ° C are usually used. For alloy strips manufactured by TRC, there is no need for a breakdown rolling step and rolling is performed at a temperature between 250 ° C and 450 ° C. Hot rolling includes the strip passing many times between rollers. After each rolling pass, before the next rolling, the sheet is typically reheated at a temperature in the range of 350-500 ° C. for about 5-10 minutes to raise the temperature before the next pass. A few cold passes with a percent reduction of 10% per pass may be used as the final rolling or sizing operation. In step 125, the process continues until the final thickness (within the set error range) is obtained. The reduction per pass can be about 20% and the total reduction can be about 80%.

  [45] After final rolling, the sheet was annealed at an appropriate temperature and time to remove the strain accumulated via static recrystallization in step. Annealing is a heat treatment process that is intended to restore ductility to alloys that have been significantly strain hardened by rolling. There are three stages of annealing heat treatment—recovery, recrystallization, and grain growth. During recovery, the physical properties of the alloy, such as conductivity, are restored, while during recrystallization, the cold-worked structure is replaced by a new set of strain-free particles. Recrystallization is recognized by metallographic methods and can be confirmed by a decrease in hardness or strength and an increase in ductility. If new strain-free particles are heated above the temperature required for recrystallization, particle growth occurs and results in a significant decrease in strength and should be avoided. The recrystallization temperature depends inter alia on the alloy composition, the initial particle size and the preceding deformation and is therefore not a constant temperature. For practical purposes, the temperature is defined as the temperature at which a highly strain-hardened (cold-worked) alloy will completely recrystallize within one hour.

  [46] The optimal annealing temperature and conditions for each alloy are determined by exposing the alloy to various temperatures for up to 1 hour, then measuring the hardness and determining the approximate temperature at which recrystallization is complete and particle growth begins. Specified by creating an annealing curve for. This temperature may also be specified as the inflection point of the hardness-anneal temperature curve. This method makes it possible to obtain the optimum temperature easily and reasonably accurately.

  [47] The annealed strip was then quenched with a suitable medium, such as water.

  [48] A series of experiments were conducted to test the comparative advantages of the described alloy embodiments and to demonstrate the low temperature formability of alloys that have been fabricated to form sheet products.

  [49] Several alloy compositions were formed and tested in these experiments, including alloys developed according to the present invention (B1-B13) and comparative samples (AZ31 and T4-Al6016). Table 1 summarizes the composition of each of the tested alloy compositions.

[50]

  [51] Each sheet of the alloy composition was manufactured using the method described above. In these experiments, the individual elements were mixed and melted in a high frequency induction melting furnace using a mild steel crucible at about 760 ° C. under an argon atmosphere. The homogenization treatment was performed at a temperature in the range of 300-500 ° C. depending on the alloy composition. The homogenization process was followed by a water quench step. The homogenized ingot was machined into a 5 mm thick strip and then hot rolled at a temperature in the range of 350-500 ° C. The thickness reduction per pass was about 20%, and the total thickness reduction was about 80%. After each rolling pass and before the next rolling, the sheet was reheated at a temperature in the range of 350-500 ° C. for about 5-10 minutes. After final rolling, the sheet was subjected to an annealing treatment to remove the accumulated strain through static recrystallization.

  [52] These sheets were then mechanically tested as described in the following examples.

Example 1: Mechanical properties at room temperature
[53] Tensile properties and formability of the as-annealed sheets of developed alloys (B1-B16) and control samples (AZ31 and T4-Al6016) were evaluated at room temperature.

[54] Each as-annealed sheet of the examined alloy composition (see Table 1) was rolled in the rolling direction using a screw-driven Instron 4505 device at a strain rate of 10 ⁻³ / s at room temperature. Tested along. The thickness of each tensile sample was about 1 mm, and the gauge distance was about 10 mm. In order to evaluate the room temperature formability of the developed alloy by a mini deep drawing test with a 6 mm diameter punch, the sample was further rolled to a thickness of 0.5 mm. The diameters of the annealed disks were 9, 9.5, 10, 10.5, 11.5, 13.1, and 14.6 mm. The critical deep drawing ratio (LDR) is defined as the ratio of the maximum disk diameter that could be fully drawn without breakage to the punch diameter. In conclusion, a high LDR value represents better moldability and a low “LDR value indicates insufficient moldability.

  [55] Table 2 summarizes the mechanical properties at room temperature of the developed alloy sheets (B1-B13) and comparative alloys (AZ31 and Al6016). Obtained tensile stress-strain curves for as-annealed Mg-Zn-Gd-Ca-Zr systems, including B1, B2, B3, B4, and B5 alloy sheets and comparative or benchmark AZ31 and Al6016 alloy sheets As shown in FIG.

  [56] The Mg-Zn-Gd-Ca-Zr type alloy sheet showed significantly higher ductility compared to the ductility of the AZ31 alloy sheet. The total elongation and LDR value of the B1 alloy sheet reached about 32% and 1.93, respectively. When 0.2% Ca is added to the B1 alloy, the total elongation can be further improved from 32% to 38%, the strength can be increased from 141 MPa to 152 MPa, and the LDR value can be increased from 1.93 to 2.02. There was found. It is noteworthy that the formability, ductility, and strength of the B2 alloy sheet is superior to that of the 6016 alloy sheet. When the Ca content was increased from 0.2% to 0.5% (B3 alloy), the ductility of the B3 alloy sheet decreased to 33% and the LDR decreased to 1.87. The above results indicate that Ca is essential for improving the formability and strength of Mg-Zn-Gd-Ca-Zr alloy, but requires strict control of the Ca content, otherwise the opposite result Will bring. Similarly, when 0.1% Sr or 0.1% La is further added to the B2 alloy, the strength is increased, but the ductility and formability are reduced.

  [57] Previously, Mg-Ca type alloys were considered brittle and therefore were not considered suitable candidates for making sheets. However, in this study, the dilute addition of Zn (0.4%) to the Mg-0.8Ca alloy greatly improved the formability in addition to the rollability and ductility, and Mg-0.8Ca-0.4Zn. It has been found that the type of alloy sheet can be made ideal for many industrial applications.

  [58] In these examples, alloy sheets formed from eight different Mg-0.8Ca-0.4Zn type alloys (B6-B13) were tested. Table 2 shows the mechanical properties of B6 to B13. Comprehensively, B13 (Mg-0.8Ca-0.4Zn-0.1Sr-0.4Gd-0.5Zr) is one of all Mg-Ca-Zn- (Zr) type alloy sheets. The best mechanical properties were given in terms of ductility (23%), moldability (1.83 LDR) and yield strength (137 MPa).

  [59] The above mechanical test results show that Mg-Zn-Gd-Ca-Zr and Mg-Ca-Zn- (Zr) type alloy sheets have higher ductility and formability than AZ31 alloy sheets. Is shown. In particular, the ductility, formability and strength of Mg-Zn-Gd-Ca-Zr type alloy sheets can even compete with those of Al6016 alloy, making these alloys suitable for a wide range of commercial applications. It is ideal.

[60]

Example 2:
[61] Annealed Mg—Ca—Zn— (Zr) type alloy sheet was age hardened by heating in silicone oil at 150 ° C. for a period sufficient to obtain maximum precipitation hardening.

  [62] The aging response was measured by Vickers hardness and tensile tests. The tensile properties and formability of the age-hardened sheet were evaluated at room temperature.

  [63] The aging curve of Mg—Ca—Zn— (Zr) type alloy sheet with aging temperature of 150 ° C. after solution treatment (400 ° C. for 0.5 hour) is plotted in FIG.

  [64] It has been found that Mg—Ca—Zn— (Zr) type alloy sheets not only have excellent ductility and formability, but also have age hardening response characteristics. In other words, after the sheet is manufactured, the strength of these alloy sheets can be further improved by aging treatment at 150 ° C. As shown in FIG. 3 and Table 3, the hardness value of the B6 alloy sheet was 46 VHN before aging. However, after aging at 150 ° C. for 30 hours, the B6 alloy sheet reached peak aging up to 58 VHN with a hardness increment of 12 VHN. On the other hand, the time to reach peak aging was extended to 72 hours when 0.4% Gd was added to the B6 alloy, and was shortened to 12 hours when 0.3% Al was added to the B6 alloy. Adding dilute Gd or Al to the B6 alloy only changed the time to reach peak aging, and the peak hardness value remained the same. Furthermore, when 0.5% Zr or 0.1% Sr was added to the B6 alloy, the peak hardness and the time required for heat treatment did not change clearly.

  [65] Table 4 shows an overview of tensile properties of Mg—Ca—Zn— (Zr) type alloy sheets under peak aging conditions. By T6 treatment (artificial aging was performed following solution treatment), the yield strength of the B6 alloy sheet was 128 MPa to 153 MPa, the B7 alloy sheet was 125 MPa to 146 MPa, the B8 alloy sheet was 123 MPa to 163 MPa, and the B9 alloy The sheet increased from 128 MPa to 164 MPa, the B10 alloy sheet increased from 137 MPa to 166 MPa, the B11 alloy sheet increased from 132 MPa to 174 MPa, the B12 alloy sheet increased from 129 MPa to 166 MPa, and the B13 alloy sheet increased from 137 MPa to 168 MPa. The UE, TE, and SHE of the Mg—Ca—Zn— (Zr) type wrought alloy sheet decreased as expected. In this regard, the ductility decreased slightly, and taking the B13 alloy sheet as an example, the ductility of the B13 alloy sheet decreased from 23% (annealed state) to 19% (peak aging state).

[66]

[67]

Example 3
[68] The above results indicate that the B2 alloy sheet exhibits the best ductility and formability among the Mg-Zn-Gd-Ca-Zr systems. Therefore, to further improve the mechanical properties of the alloy sheet, two important processing parameters were adjusted that should affect the performance of the sheet: rolling temperature and annealing conditions.

  [69] Various hot rolling and annealing conditions were performed on the B2 alloy sheet using the methods and experimental equipment described above to determine thermomechanical process parameters for optimized mechanical properties. Tables 5 and 6 summarize the tensile properties of the as-annealed sheets of these two alloys produced under various thermomechanical process conditions.

  [70] During the annealing process, recrystallization can refine the particle size, remove defects caused by plastic deformation, and weaken the texture. As a result, the ductility and formability of the annealed sheet was significantly increased compared to the as-rolled one. Experimental results show that recrystallization can occur in the temperature range of 350 ° C to 500 ° C. If the hardness is no longer apparently reduced by extending the annealing time at a certain annealing temperature, the recrystallization is complete.

  [71] Since the final mechanical properties were closely related to the annealing temperature and time, the B2 alloy sheet was selected to optimize the annealing conditions. The optimum annealing conditions for the alloy sheet were identified by measuring the change in hardness after exposure at various temperatures for various times. Therefore, in order to find the recrystallization completion time at various annealing temperatures, a hardness test of B2 alloy sheet samples having various annealing temperatures and annealing times was performed.

  [72] The change in hardness as a function of exposure time for a B2 sheet rolled at 450 ° C. and subsequently annealed at various temperatures is shown in FIG. The hardness value decreases rapidly with the first one-minute anneal and is 1 hour at 350 ° C., 0.5 hour at 400 ° C., 0.5 hour at 450 ° C. It was found that the temperature became stable after 0.5 hours at ℃. Therefore, the sheet was annealed at 350 ° C. for 1 hour, 400 ° C. for 0.5 hour, 450 ° C. for 0.5 hour, and 500 ° C. for 0.5 hour, and then tested along the rolling direction. With increasing annealing temperature, the yield strength of B2 alloy sheets decreased as expected, while the strain hardening index of these alloys increased slightly. Note that the UE and SHE of the B2 alloy sheet decreased after annealing at 500 ° C. for 0.5 hour.

  [73] Further, as shown in Table 5, the recrystallization time of the B2 alloy sheet is 1 hour when the annealing temperature is 350 ° C. However, when the annealing temperature is 400, 450 and 500 ° C., the recrystallization time of the B2 alloy sheet is 0.5 hour.

  [74] Also, room temperature tensile tests were performed on B2 alloy sheets annealed under various conditions of 350 ° C for 1 hour, 400 ° C, 450 ° C and 500 ° C for 0.5 hour. Table 6 summarizes the mechanical properties including yield strength, UTS, UE, TE, and SHE of the B2 alloy sheet under various annealing conditions. For the B2 alloy sheet, annealing at 400 ° C. for 0.5 hours resulting in 38% ductility has proven to be the optimal annealing condition.

[75]

[76]

  [77] Taking into account the UE and SHE values, hot rolling at 450 ° C. and annealing at 400 ° C. for 0.5 hour provides the best formability for both alloys.

Conclusion
[78] Overall, experimental results conclude that Mg-Ca-Zn- (Zr) type alloys show moderate formability, but these can be significantly strengthened by artificial aging treatment be able to. For example, the yield strength of an as-annealed Mg-0.8Ca-0.4Zn-0.1Sr-0.4Gd-0.5Zr alloy is only about 137 MPa, but the application of an aging treatment at 150 ° C. Can be increased to 168 MPa.

  [79] The inventors have also found that sheets formed from Mg-Zn-Gd-Ca-Zr type alloys exhibit superior mechanical properties in terms of strength and formability. Addition of 0.2% Ca to Mg-1Zn-0.4Gd-0.5Zr alloy results in formability (from 1.93 LDR to 2.02 LDR) and strength (from 141 MPa to 152 MPa) of the resulting alloy sheet Was found to result in a significant increase in. When the Ca content is increased to 0.5%, there is a slight increase in yield strength (yield strength) from 152 MPa to 155 MPa compared to the Mg-1Zn-0.4Gd-0.2Ca-0.5Zr alloy. However, the LDR value dropped from 2.02 to 1.87. The results show that elemental Ca is essential for improving the formability and strength of the Mg—Zn—Gd—Ca—Zr alloy sheet, but it is necessary to strictly control the Ca content. When 0.1% Sr or 0.1% La was further added to the Mg-1Zn-0.4Gd-0.2Ca-0.5Zr alloy, the strength increased, but the LDR value decreased.

  In addition to the [80] Mg—Zn—Gd—Ca—Zr alloy, the Mg—Ca—Zn—Sr— (Gd) —Zr alloy sheet also showed sufficient strength and formability at room temperature. The Mg-0.8Ca-0.4Zn-0.1Sr-0.4Gd-0.5Zr composition showed the best mechanical properties in terms of yield strength (137 MPa) and formability (1.83 LDR).

  [81] In summary, the present invention relates to the development of magnesium alloys and the resulting highly formable magnesium alloy sheets. When the alloying element Ca is added to the Mg—Zn—RE—Zr alloy, the ductility and formability of each alloy sheet can be remarkably improved. More specifically, the addition of a small amount of Ca to an Mg—Zn—Gd—Zr type alloy results in a new Mg alloy sheet having high ductility, formability, and reasonably good strength. In this regard, (1) When dilute calcium was added to the Mg—Zn—Gd—Ca—Zr system, the ductility and formability were substantially improved. (2) The Mg-Ca-Zn- (Zr) type alloy also showed excellent ductility and formability by adding a small amount of alloying elements. The ductility and formability of sheets formed from these novel alloys are far superior to the currently used AZ31 and can be comparable to 6016 alloy sheets, and the alloys and their corresponding alloy sheets are: It is suitable for many industrial applications.

  [82] We believe that the above features make the alloys of the present invention particularly suitable for automotive applications. In addition, the alloys of the present invention can be processed by a series of existing production techniques including extrusion, forging and twin roll casting.

  [83] Those skilled in the art will appreciate that the invention described herein is amenable to variations and modifications that can be introduced into the combination of compositions and steps other than those specifically described. Will do. It should be understood that the invention includes all such variations and modifications as fall within the spirit and scope of the invention.

  [84] The terms "comprise", "comprises", "comprised" or "comprising" are used herein (including the claims). As used herein, these terms specify the presence of a presented feature, whole number / integers, step or component, but one or more other features, whole number / integer, It is not to be construed as excluding the presence of steps, ingredients, or groups thereof.

  [85] Future patent applications may be filed in Australia or abroad based on this application, or may be priority claims from this application. It is understood that the following provisional claims are provided by way of example and do not limit the scope of what might be claimed in any such future application. At a later date, features may be added to or deleted from the provisional claims to further define or redefine one or more of the present inventions.

Claims (25)

(Wt%):
0.1 to 2.0 Zn,
0.05 to 1.5 Ca,
0.1 to 1.0 Zr,
0 to 1.3 rare earth elements containing Gd or Y or mixtures thereof,
0-0.3 Sr,
0 to 0.7 Al,
Magnesium type wrought alloy consisting essentially of the balance Mg and other inevitable impurities.   The alloy according to claim 1, wherein the rare earth element mixture comprises gadolinium or yttrium and a lanthanide series rare earth element.   The alloy according to claim 1 or 2, wherein the rare earth element mixture contains gadolinium and La.   3. An alloy according to claim 1 or 2, wherein the rare earth element consists essentially of gadolinium. (Wt%):
Zn: 0.1-2.0,
Ca: 0.05 to 1.5,
Zr: 0.1 to 1.0,
Gd: 0 to 1.0,
Sr: 0 to 0.3,
La: 0 to 0.3,
Al: Magnesium-type wrought alloy consisting essentially of 0-0.7 and the balance Mg and other inevitable impurities. (Wt%):
Zn: 0.3 to 1.0
Ca: 0.3 to 1.0,
Zr: 0.2 to 0.7,
Gd: 0.1 to 0.5,
Sr: 0 to 0.2,
La: 0 to 0.2,
Magnesium-type extension alloy according to any one of claims 1 to 5, consisting essentially of Al: 0 to 0.5 and the balance Mg and other inevitable impurities. (Wt%):
Zn: 0.5 to 2.0,
Ca: 0.05 to 1.0,
Zr: 0.1 to 1.0,
Gd: 0.05 to 1.0
Sr: 0 to 0.3,
La: 0 to 0.3,
Al: 0 to 0.7, and Mg-Zn-Gd-Ca-Zr type alloys consisting essentially of the balance Mg and other inevitable impurities. Magnesium type wrought alloy. (Wt%):
Zn: 0.5 to 1.5,
Ca: 0.1 to 0.7,
Zr: 0.2 to 0.7,
Gd: 0.1 to 0.5,
Sr: 0 to 0.2,
La: 0 to 0.2,
8. Magnesium-type extension according to claim 7, comprising an alloy of Mg-Zn-Gd-Ca-Zr type consisting essentially of Al: 0.2-0.5 and the balance Mg and other inevitable impurities. Alloy. (Wt%):
Ca: 0.3 to 1.5,
Zn: 0.1-0.8,
Zr: 0.1 to 1.0,
Gd: 0 to 1.0,
Al: 0 to 0.7,
Sr: 0-0.3, and Mg-Ca-Zn- (Zr) type alloys consisting essentially of the balance Mg and other inevitable impurities. Magnesium type wrought alloy. (Wt%):
Ca: 0.6 to 1.0,
Zn: 0.3-0.5,
Zr: 0.2 to 0.7,
Gd: 0 to 0.5,
Al: 0.2 to 0.5,
Magnesium-type wrought alloy according to claim 9, comprising a Mg-Ca-Zn- (Zr) type alloy consisting essentially of Sr: 0-0.2 and the balance Mg and other inevitable impurities .   Magnesium-type extension alloy according to any of the preceding claims, wherein the total weight percent of alloying elements is less than 4%, preferably less than 3%.   Magnesium-type extension alloy according to any of the preceding claims, further comprising 0.05 to 0.7 Mn, preferably 0.1 to 0.5 Mn.   Magnesium-type extension alloy according to any of the preceding claims, wherein the magnesium-type alloy contains less than 0.5% by weight of incidental impurities.   Magnesium-type extension alloy according to any of the preceding claims, wherein the magnesium-type alloy contains less than 0.2% by weight of incidental impurities.   Selected from one of Mg-1Zn-0.4Gd-0.2Ca-0.5Zr, or Mg-0.8Ca-0.4Zn-0.1Sr-0.4Gd-0.5Zr, Magnesium-type wrought alloy according to any of claims.   A magnesium type extension alloy sheet comprising at least one magnesium type extension alloy according to any one of claims 1 to 15. A method for producing a magnesium type alloy sheet product,
Preparing a magnesium alloy melt from the magnesium-type alloy according to any one of claims 1 to 15;
Casting the magnesium alloy melt into a slab or strip according to a predetermined thickness;
Homogenizing or preheating the cast slab or strip;
Subsequently, in order to reduce the thickness of the homogenized slab or strip, the homogenized or preheated slab or strip is hot-rolled at an appropriate temperature to produce an alloy sheet product of a predetermined thickness. And steps to
Annealing the alloy sheet product for a time at an appropriate temperature;
Including a method.   The method of claim 17, wherein casting comprises feeding a magnesium alloy melt between the rolls of a twin roll caster to create a strip.   19. A method of making a magnesium-type alloy sheet product according to claim 17 or 18, wherein the homogenization or preheating of the cast slab or strip occurs at a temperature between 300 and 500C.   20. A method for producing a magnesium-type alloy sheet product according to any one of claims 17 to 19, wherein homogenization or preheating of the cast slab or strip is followed by quenching, preferably water quenching.   The method for producing a magnesium-type alloy sheet product according to any one of claims 17 to 20, wherein the hot rolling is performed in a temperature range of 300 to 550 ° C, preferably 350 to 500 ° C.   A method for producing a magnesium-type alloy sheet product according to any one of claims 17-21, wherein the hot rolling results in a total thickness reduction of 50-95%, preferably 70-80%.   Hot rolling is performed using a plurality of rolling passes, wherein after each rolling pass, the sheet is reheated at a temperature in the range of 350-500 ° C before the next rolling. A method for producing a magnesium-type alloy sheet product according to any one of claims 22 to 22.   24. Magnesium according to any one of claims 17 to 23, wherein casting comprises pouring the magnesium alloy melt directly into one of a chill (DC) caster, a sand caster, or a mold caster. A method of making mold alloy sheet products.   25. Producing a magnesium-type alloy sheet product according to any one of claims 17 to 24, further comprising the step of subjecting the annealed alloy to an age hardening treatment comprising heating the alloy for at least 1 hour at 150 ° C. how to.

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