Patent Application
20250144704
This application claims the benefit of Chinese Patent Application No. 202311459141.5, filed on Nov. 3, 2023. The entire disclosure of the application referenced above is incorporated herein by reference.
The information provided in this section is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
The present disclosure relates to magnesium alloys, and in particular to magnesium alloys with improved castability, compared with conventionally used alloys such as AZ91D, and in particular improved castability by thixomolding.
Alloy AZ91D is one of the most widely used magnesium die cast alloys because of its combination of mechanical properties, corrosion resistance, and castability. (AZ91D is nominally 8.2-9.7 wt % Al, 0.35-1.0 wt % Zn, <0.1 wt % silicon, and the balance Mg). However, an issue with existing magnesium alloys such as AZ91D is their susceptibility to hot tearing and cold shut defects in the die cast parts made from the alloys.
Hot tears are discontinuities that occur during casting operations as the material being cast solidifies. Hot tears occur when the material experiences some force or restraint during the solidification stage of a casting operation, i.e., when the material being cast is part solid and part liquid. A hot tear can occur because as a material solidifies, it contracts, and a force or restraint impeding this contraction can cause the material to “tear.”
A cold shut is a defect resulting from the cooling of the surfaces of liquid metal during casting when two fronts of the liquid metal meet and do not fuse properly in the mold cavity, leaving a weak spot or crack.
Current strategies to try to control defects like hot tears and cold shuts include sophisticated control processes to manage heat loss during the casting operation, but in many cases defects continue to occur resulting in reduced yield rates. In some cases, it may even be necessary to redesign the part to achieve a commercially acceptable yield,
The present disclosure provides magnesium alloys with less susceptibility to casting defects such as hot tears and cold shuts, and diecast magnesium alloy parts made from such alloys.
Generally, the magnesium alloys according to this disclosure are specially adapted for die casting, and in particular for thixomolding, with a low incidence of defects (as compared to widely used commercial magnesium alloys). The alloy generally comprises between about 9.8 wt % and about 15 wt % Al, greater than 0 and less than about 1.5 wt % zinc; and greater than 0 and less than about 1.0 wt % silicon. The balance of the alloy is magnesium and impurities. There are optionally no more than about 0.15 wt % of impurities, with no single impurity comprising more than about 0.05 wt %. Optionally, there is at least 0.1 wt % Zn, and at least about 0.5 wt % Si.
In a first embodiment of the alloys of this disclosure, the aluminum content is between about 10 wt % and about 13 wt % Al, and other constituents are between about 0.1 wt % and 1.5 wt % Zn; and between about 0.5 wt % and 1.0 wt % Si. The alloy of the first embodiment may have a Crack Susceptibility Index (CSI), as defined below, similar to that of common aluminum casting alloys such as a356, or about 250 or lower.
In a second embodiment of the alloys of this disclosure, the aluminum content is between about 13 wt % and 15 wt % Al, and other constituents are between about 0.1 wt % and 1.5 wt % zinc; and between about 0.5 wt % and 1.0 wt % silicon. The alloy of the second embodiment preferably has a CSI similar to that of common aluminum casting alloys such as a356, or about 250 or lower.
Some embodiments of this disclosure provide a magnesium diecast part, and in particular a magnesium part made by thixomolding. The part is made of an alloy comprising between about 10 wt % and about 15 wt % Al; between about 0.1 wt % and 1.5 wt % Zn; and between about 0.5 wt % and 1.0 wt % Si, and the balance Mg and impurities. There are preferably no more than about 0.15 wt % of impurities, with no single impurity comprising more than about 0.05 wt %.
Further areas of applicability of the present disclosure will become apparent from the detailed description, the claims and the drawings. The detailed description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the disclosure.
The present disclosure will become more fully understood from the detailed description and the accompanying drawings, wherein:
In the drawings, reference numbers may be reused to identify similar and/or identical elements.
The present disclosure provides magnesium alloys with less susceptibility to casting defects such as hot tears and cold shuts, as compared to current commercially used magnesium allows such as AZ91D, and to diecast magnesium alloy parts made from these alloys.
Generally, the magnesium alloys according to this disclosure are specially adapted for die casting, and in particular (but not exclusively) for thixomolding, with a low incidence of defects such as hot tears and cold shuts. Thixomolding or magnesium injection molding is a single-step, semi-solid molding process in which chips of a magnesium alloy are fed into a heated screw and barrel, then thermally and mechanically processed into a semi-solid state and injected directly into a tool cavity.
The alloys of this disclosure generally comprise aluminum greater than or equal to about 10 wt % and less than or equal to about 15 wt %, zinc greater than 0 and less than or equal to about 0.5 wt %; silicon greater than 0 and less than or equal to about 1.5 wt %, with the balance being magnesium and impurities. There can be up to about 0.15 wt % of additional elements, with no single additional element comprising more than about 0.05 wt %. Optionally, there is at least 0.1 wt % Zn, and at least about 0.5 wt % Si.
A Crack Susceptibility Index or CSI has been proposed as an indicator of when a magnesium alloy is subject to cracking such as hot tears. See, Lie and SIndo, “Susceptibility of Magnesium Alloys to Solidification Cracking,” Science and Technology of Welding and Joining 25.3 (2020): 251-257, the entire disclosure of which is incorporated herein by reference. The CSI is the maximum slope of the temperature versus the square root of the fraction of solid (fs) over the range of interest.
The inventors have found that zinc increases the CSI and can be detrimental to hot tearing resistance.
The inventors have found that aluminum does not have a significant impact on CSI or on tearing resistance at levels of 9 wt % or greater. However, as shown in
The inventors have found that silicon does not have a significant impact on CSI or on tearing resistance. However, as shown in
A first embodiment of the alloys of this disclosure comprises aluminum greater than or equal to about 10 wt % and less than or equal to about 13 wt %; zinc in an amount greater than 0 and less than or equal to about 0.5 wt %; and silicon in an amount greater than 0 and less than or equal to about 1.5 wt %, with the balance being magnesium and impurities. In some versions of the first embodiment the zinc content is greater than or equal to about 0.1 wt % and less than or equal to about 0.5 wt %. In some versions of the first embodiment the silicon content is greater than or equal to about 0.5 wt % and less than or equal to about 1.0 wt %. The alloys of this first embodiment typically have a CSI of less than 250.
In a second embodiment of the alloys of this disclosure, the aluminum content is greater than or equal to about 13 wt % and less than or equal to 15 wt %, zinc in an amount greater than 0 and less than or equal to about 0.5 wt %; and silicon in an amount greater than 0 and less than or equal to about 1.5 wt %, with the balance being magnesium and impurities. In some versions of the first embodiment the zinc content is greater than or equal to about 0.1 wt % and less than or equal to about 0.5 wt %. In some versions of the first embodiment the silicon content is greater than or equal to about 0.5 wt % and less than or equal to about 1.0 wt %. The alloys of this second embodiment typically have a CSI of less than 250, and owing to their greater aluminum content than the first embodiment, have a lower liquidus temperature.
Some embodiments of this disclosure provide a diecast part, and in particular a part made by thixomolding. The part is made of an alloy comprising aluminum greater than or equal to about 10 wt % and less than or equal to about 15 wt %, zinc in an amount greater than 0 and less than or equal to about 0.5 wt %; and silicon in an amount greater than 0 and less than or equal to about 1.5 wt %, with the balance being magnesium and impurities. There are preferably no more than 0.15 wt % of additional elements, with no single additional element comprising more than 0.05 wt %.
In a first embodiment of the parts of this disclosure, there is between about 10 wt % and about 13 wt % Al, zinc in an amount greater than 0 and less than or equal to about 0.5 wt %; and silicon in an amount greater than 0 and less than or equal to about 1.5 wt %, with the balance being magnesium and impurities. In some versions of the first embodiment the zinc content is greater than or equal to about 0.1 wt % and less than or equal to about 0.5 wt %. In some versions of the first embodiment the silicon content is greater than or equal to about 0.5 wt % and less than or equal to about 1.0 wt %. The alloys of this first embodiment typically have a CSI of less than 250.
In a second embodiment of the alloys of this disclosure the aluminum content is greater than or equal to about 13 wt % and less than or equal to 15 wt %, zinc in an amount greater than 0 and less than or equal to about 0.5 wt %; and silicon in an amount greater than 0 and less than or equal to about 1.5 wt %, with the balance being magnesium and impurities. In some versions of the first embodiment the zinc content is greater than or equal to about 0.1 wt % and less than or equal to about 0.5 wt %. In some versions of the first embodiment the silicon content is greater than or equal to about 0.5 wt % and less than or equal to about 1.0 wt %. The alloys of this second embodiment typically have a CSI of less than 250 and owing to their greater aluminum content than the first embodiment, have a lower liquidus temperature.
The foregoing description is merely illustrative in nature and is in no way intended to limit the disclosure, its application, or uses. The broad teachings of the disclosure can be implemented in a variety of forms. Therefore, while this disclosure includes particular examples, the true scope of the disclosure should not be so limited since other modifications will become apparent upon a study of the drawings, the specification, and the following claims. It should be understood that one or more steps within a method may be executed in different order (or concurrently) without altering the principles of the present disclosure. Further, although each of the embodiments is described above as having certain features, any one or more of those features described with respect to any embodiment of the disclosure can be implemented in and/or combined with features of any of the other embodiments, even if that combination is not explicitly described. In other words, the described embodiments are not mutually exclusive, and permutations of one or more embodiments with one another remain within the scope of this disclosure.
| Number | Date | Country | Kind |
|---|---|---|---|
| 202311459141.5 | Nov 2023 | CN | national |
