[0025] The invention provides a method for preparing a shape memory aluminum matrix composite material, comprising the following steps:
[0026] Step S1: place the shape memory alloy fiber layer and the aluminum alloy plate alternately until the preset thickness is reached, and obtain the shape memory alloy fiber and aluminum alloy plate unit to be processed; wherein, each layer of shape memory alloy fiber layer includes a plurality of Shape memory alloy fibers, the diameter of the shape memory alloy fibers is 0.1 mm to 0.2 mm, and the distance between two adjacent shape memory alloy fibers is 0.5 cm to 1.0 cm;
[0027] Step S2: hot pressing the shape-memory alloy fiber and the aluminum alloy plate unit to form a metal bond between the shape-memory alloy fiber and the aluminum alloy plate to obtain the shape-memory aluminum matrix composite material.
[0028] Compared with the prior art, in the preparation method of the shape-memory aluminum matrix composite provided by the present invention, the shape-memory alloy fiber layer and the aluminum alloy plate are alternately placed to ensure that only one layer of shape-memory alloy is placed between the two layers of aluminum alloy plates. Absorbed into layers, and each layer of shape memory alloy fiber layer includes a plurality of shape memory alloy fibers arranged at intervals, the diameter of the shape memory alloy fiber is 0.1 mm to 0.2 mm, and the distance between two adjacent shape memory alloy fibers is 0.5 cm to 1.0 cm, such a loose arrangement can make the shape memory alloy fiber fully stretched to form orientation during the hot pressing process, and embedded in the aluminum alloy plate to form a metal bond, effectively awakening the memory effect of the shape memory alloy, thereby realizing shape memory Aluminum matrix composites can return to their pre-deformed state at room temperature without heating up.
[0029] It should be noted that the core aluminum alloy plate and sandwich aluminum alloy plate, core shape memory alloy fiber and sandwich shape memory alloy fiber described in the present invention are only for the convenience of more clearly illustrating the aluminum alloy plate and aluminum alloy plate in the preparation method. In the process of alternately placing shape memory fibers, the core aluminum alloy plate and the sandwich aluminum alloy plate are the same aluminum alloy plate, and the core shape memory alloy fiber and the sandwich shape memory alloy fiber are both the same shape memory alloy fiber.
[0030] On the basis of ensuring the shape memory aluminum matrix composite material, in order to ensure the mechanical strength of the shape memory aluminum matrix composite material, the thickness of the aluminum alloy plate is preferably 1.5-3 mm. In the shape memory aluminum matrix composite material of the present invention, the aluminum alloy plate is the main body, the shape memory alloy fiber is the reinforcing phase, the thickness of the aluminum alloy plate determines the mechanical strength of the shape memory aluminum matrix composite material, and the thickness of the aluminum alloy plate is limited It is 1.5-3mm, which can ensure that the obtained shape memory aluminum matrix composite material has good mechanical strength, so that when it is subjected to a small stress, the mechanical properties provided by the aluminum alloy plate can ensure that the shape memory aluminum matrix composite material will not deform. When deformed under a large stress, the shape memory alloy fiber can exert a "memory effect" and restore it to the state before deformation. In addition, limiting the thickness of the aluminum alloy plate to 1.5-3 mm can also make the shape-memory aluminum-based composite material lighter in weight on the basis of good mechanical properties.
[0031] In order to simplify the process of arranging the shape memory alloy fibers on the aluminum alloy plate, the alternate placement of the shape memory alloy fiber layer and the aluminum alloy plate in step S1 specifically includes the following steps:
[0032] Step S11: see figure 1 , the core layer shape memory alloy fiber 2 is wound on a core layer aluminum alloy plate 1 to obtain a core layer aluminum alloy unit. Two layers of shape memory alloy fibers on the surface;
[0033] Step S12: see figure 2 A sandwich aluminum alloy plate 3 is placed on the upper surface and the lower surface of the core aluminum alloy unit respectively to obtain a sandwich aluminum alloy unit. The sandwich aluminum alloy unit includes three layers of aluminum alloy plates and is sandwiched between the three layers of aluminum alloy plates Two layers of shape memory alloy fibers in between;
[0034] Step S13: see image 3 , the sandwich shape memory alloy fiber 4 is wound on the sandwich aluminum alloy unit to obtain the shape memory alloy fiber to be processed and the aluminum alloy plate subunit, the shape memory alloy fiber to be processed and the aluminum alloy plate subunit include four layers of shape memory alloy fiber and the sandwich Three layers of aluminum alloy plates between four layers of shape memory alloy fibers;
[0035] Step S14: return to S12 until the shape memory alloy fiber to be processed and the aluminum alloy plate subunit reach the preset thickness, and the shape memory alloy fiber to be processed and the aluminum alloy plate unit are obtained.
[0036]Using the shape-memory alloy fiber and aluminum alloy plate unit to be processed obtained in steps S11-S14 can ensure that only one layer of shape-memory alloy fiber is arranged between two layers of aluminum alloy plates, avoiding the tight arrangement caused by the lamination of multiple layers of shape-memory alloy fibers , the problem that the fibers cannot be fully stretched. In addition, the aluminum alloy plate is used as the winding body, and the continuous shape memory alloy fibers are stretched and wound on the aluminum alloy plate, which can ensure a more orderly arrangement of the shape memory alloy fibers and improve the consistency of the overall performance of the shape memory aluminum matrix composite.
[0037] In order to make the shape memory alloy and the aluminum alloy plate fully contact to form a metal bond, and improve the overall performance of the shape memory aluminum matrix composite material, before step S1, the preparation method further includes, separately performing preprocessing;
[0038] The pretreatment of the aluminum alloy plate includes: sequentially grinding and polishing the surface of the aluminum alloy plate, acid etching for 45s~60s, cleaning and drying;
[0039] The pretreatment of the shape memory alloy fiber includes: sequentially grinding and polishing the surface of the shape memory alloy fiber, acid etching for 20s-30s, cleaning and drying.
[0040] Among them, grinding and polishing the aluminum alloy plate and the shape memory alloy fiber respectively can remove the oxide layer on the surface of the aluminum alloy plate and the shape memory alloy fiber, so that the acid etching in the next step is more sufficient.
[0041] The acid etching process is essentially a process of increasing the surface area of the aluminum alloy plate and the shape memory alloy fiber. After the acid etched aluminum alloy plate and the shape memory alloy fiber are fully contacted in the subsequent hot pressing process, more metal bonds can be formed. The combination of the aluminum alloy plate and the shape memory alloy fiber is tighter, and the overall performance of the shape memory aluminum matrix composite is improved.
[0042] For the hot-pressing process of step S2, the temperature of hot-pressing, the pressure of hot-pressing and the time of hot-pressing are important process conditions for whether the shape memory alloy fiber can be fully stretched and whether the aluminum alloy plate and the shape memory alloy fiber can be fully combined , the temperature of hot pressing is preferably 500°C to 600°C, the pressure of hot pressing is preferably 30KPa to 40KPa, and the time of hot pressing is preferably 3h to 4h, using the shape memory aluminum matrix composite material prepared under the above process conditions, the shape memory The alloy fiber stretches more fully, and the combination between the aluminum alloy plate and the shape memory alloy fiber is tighter, and the shape memory aluminum matrix composite can return to the state before deformation more quickly after deformation.
[0043] The present invention also provides a shape-memory aluminum-based composite material, which is prepared by the above-mentioned preparation method.
[0044] In order to ensure that the shape memory alloy fibers can be further fully stretched, the volume fraction of the shape memory alloy fiber layer in the shape memory aluminum matrix composite material is preferably 0.026%-0.401%. The volume fraction of the shape memory alloy fiber layer in the shape memory aluminum matrix composite is limited to 0.026% to 0.401%, and each layer of shape memory alloy fiber layer is very thin, so that the shape memory alloy The fibers are further fully stretched, thereby further improving the recovery speed of the shape memory aluminum matrix composite material after deformation. Moreover, shape memory alloy fibers are expensive, and limiting the volume fraction of shape memory alloy fiber layers can reduce the amount of shape memory alloy fibers used and reduce the production cost of shape memory aluminum matrix composites on the basis of ensuring shape memory performance.
[0045] Regarding the selection of shape memory alloy fiber materials, existing shape memory alloy fibers include TiNi-based shape memory alloy fibers, copper-based shape memory alloy fibers and iron-based shape memory alloy fibers. Among them, TiNi-based shape memory alloy fibers and copper-based shape memory alloy fibers have been put into practical use. The shape memory alloy fibers of the present invention are preferably TiNi-based shape-memory alloy fibers or copper-based shape-memory alloy fibers that have been put into practical use.
[0046] The shape-memory alloy fiber of the present invention is further preferably TiNi-based shape-memory alloy fiber. The TiNi-based shape-memory alloy fiber has the characteristics of strong memory effect and superelasticity, stronger recovery ability after deformation, and faster recovery speed.
[0047] The molar ratio of Ti to Ni in the TiNi shape memory alloy fiber directly affects the shape memory effect of the TiNi shape memory alloy fiber. Further, the molar ratio of Ti to Ni in the TiNi shape memory alloy fiber is preferably 0.95:1 to 1:1, In this way, the obtained shape-memory aluminum matrix composite can quickly return to the original state before deformation at room temperature without any heat treatment. In order to further improve the recovery speed of the shape memory aluminum matrix composite after deformation, the molar ratio of Ti to Ni is further preferably 1:1.
[0048] The present invention also provides a middle frame of a mobile terminal, which is made of a shape-memory aluminum-based composite material.
[0049] It should be noted that the shape-memory aluminum-matrix composite material used in making the middle frame of the above-mentioned mobile terminal may be the shape-memory aluminum-matrix composite material provided by the present invention, which will not be described in detail here.
[0050] Further, the present invention also provides a method for making a middle frame of a mobile terminal, which is used for making a middle frame of a mobile terminal.
[0051] see Figure 4 , the manufacturing method of the middle frame of the mobile terminal comprises the following steps:
