JPS627837A - Manufacture of magnesium alloy having fine-grained structure - Google Patents

Abstract

PURPOSE:To provide a fine-grained structure by allowing a plastic working stage of a specific working temp. and rate of strain to be included in the process of manufacturing a magnesium-base alloy containing specific amounts of Zr. CONSTITUTION:The magnesium-base alloy is made by incorporating as principal hardener 0.2-0.8wt.% Zr to a known alloy of Mg-Zn, Mg-Al-Zn or another type containing 1 or >=2 elements among Zn, Al and Mn. In the manufacturing process of the above alloy, the plastic working stage of 150-450 deg.C working temp. and 1X10<-4>sec<-1>-1sec<-1> rate of strain is included.

Description

[Detailed Description of the Invention] Industrial Fields of Use This invention has a fine grain structure and is suitable for forming, forging,
The present invention also relates to a method for producing a superplastic magnesium alloy that exhibits excellent ductility and is suitable for other uses such as structural materials.

Conventional magnesium alloys have a ductility as low as -1, making them unsuitable for use as materials for structures, forming, forging, and the like.

Conventionally, it has been considered to improve the ductility by making the crystal grains finer, mainly from the viewpoint of the composition of the alloy. A JIS-MT4 alloy whose ductility is improved by adding about .8 wt% of the content is well known.

Problems to be Solved by the Invention However, when a magnesium alloy as described above containing Z is used and manufactured by a manufacturing method that refines the crystal grains and includes a cold working → annealing process known as the vine manufacturing method. However, it is difficult to refine the crystal grain size to less than 20μ, and it has not been possible to obtain the desirable superplastic properties of the product.Furthermore, magnesium alloys inherently have poor cold workability. Therefore, it is desired to obtain a grain-refined structure without performing cold working, but conventional manufacturing methods have not been able to meet this requirement.

Means for Solving the Problems In view of the problems mentioned above, the inventors aimed to establish a manufacturing method that eliminates the need for cold working and can achieve ultra-fine crystal grains. As a result of various experiments and research, we found that by casting a magnesium alloy containing 7-r as a refining element and processing it under predetermined warm conditions and extremely low strain conditions, the desired purpose could be achieved. They found the means to achieve this and completed this invention.

Therefore, in the production process of the magnesium-based alloy containing 0.2 to 0.8 wt% of Zr, the present invention provides the following conditions: Processing temperature: 150 to 450°C Strain rate: 1 X'I 0-4sec- '~1
It is characterized by performing plastic working of 5ec-1.

The magnesium-based alloy used in the production of this invention is a known Mq-Zn alloy containing one or more of Zn, AI, or Mn as a main hardening element, Mg-A
This is an alloy such as 1-Zn containing Zr in a specified amount range.

Here, the Zn content is generally approximately 0.5 to 1.5w.
t% range, and the content of A1 is approximately 2.4 to 7.2
The range is wt%. In addition, Mn, Fe, and 5iXCu are contained within the allowable impurity range.

In this invention, essential additive elements include 0°2~o, a
°Zr, whose wt% content is specified, is effective in refining crystal grains as is conventionally known, and has a lower limit of 0.
If it is less than 2wt%, there is no effect, and the upper limit Q, Bwt%
If it exceeds this value, Zr-based crystallized substances will be generated, leading to a decrease in ductility. The most suitable Zr content is about 0.4 to 0.7'wt%.

The type of plastic working that must be performed during the manufacturing process of this invention is not particularly limited, and may include various types of processing such as stretching, extrusion, rolling, wire drawing, forging, and compression. This includes processing, etc. However, the processing conditions are a processing temperature of 150 to 450°C and a strain rate of T 1 X 10-4 sec-1 to 15 ec-1 (7
) limited to a range. Here, if the processing humidity is less than 150'C, dislocations generated by processing are unlikely to form cells, and solid solution Zr does not precipitate on subgrains or grains, resulting in insufficient pinning effect. It is not possible to refine the crystal grains. On the other hand, if the processing temperature exceeds 450°C, solid solution Zr will not precipitate, making it impossible to achieve grain refinement. Also, the strain rate of the alloy during processing is 'l x 10-4sec-
If it is less than 1, fine cells and fine recrystallized grains will not become small. If processing is applied at a speed exceeding 1 sec-1 per half, many dislocations will be introduced and the cell will not be stabilized, and as a result, the pinning effect by the precipitates will no longer be sufficient and grain refinement will no longer be achieved. . According to the experimental results, the most preferable range of processing conditions is generally processing temperature: 200~
250°C, hissing rate; 1 X 10-3SeC-
It is about 1 to 1 x 10-2 SeC-1.

Effects of the Invention According to the present invention, as seen in the examples below, a magnesium alloy with an extremely fine crystal grain structure with a crystal grain size of 20 μm or less can be obtained using a simple manufacturing process that does not involve cold working. Can be done. Therefore, it is possible to obtain a magnesium alloy with extremely excellent ductility without causing a decrease in mechanical strength, and it has much better formability, forgeability, etc. than the known alloys that have been provided so far. It is possible to provide a magnesium alloy material.

Incidentally, the reason why the above-mentioned fine grain structure is obtained by the manufacturing method of the present invention is that Zr in solid solution precipitates into subgrains or grains due to the processing conditions described above.
It is thought that recrystallization is delayed due to the increased pinning effect, resulting in fine crystal grains.

Examples Alloys having various compositions shown in Table 1 were cast into ingots with a diameter of 75 InIn using a water-cooled mold. Then, this ingot was heated to 450℃ for 3
The samples were extruded into strips of m The sample was subjected to plastic working at a strain rate of 1 SeC' and then annealed at 500°C.

For each sample obtained above, the average grain size in the alloy composition was measured and the mechanical properties were examined, and the results were as shown in Table 2.

Table-2

Claims (1)

[Claims] When manufacturing a magnesium-based alloy containing 0.2 to 0.8 wt% of Zr, in the manufacturing process: Processing temperature: 150 to 450°C Strain rate: 1 x 10^-^4 sec^-^ 1~1se
A method for producing a magnesium alloy having a fine grain structure, characterized by including a c^-^1 plastic working step.