JPH0372050A - Al alloy for vehicle having excellent corrosion fatigue strength - Google Patents

Abstract

PURPOSE:To obtain the Al alloy for vehicles by incorporating a JIS A No.6000 series alloy as a base with specified amounts of rare earth elements. CONSTITUTION:One or more kinds of rare earth elements are added to a JIS A No.6000 series alloy in the range of 0.05 to 0.5wt.%. By this addition, the potential difference between grain boundaries and a matrix is reduced to suppress intergranular corrosion and the corrosive shape is changed from intergranular corrosion to plannar corrosion. In this way, the Al alloy for vehicles having excellent corrosion fatigue strength appropriately used as a structural material for vehicles to be subjected to repeated stress in a corrosive environment can be obtd. In the case of <0.05% amt. of rare earth elements to be added, the effect for suppressing intergranular corrosion is not sufficient and the change of the corrosive shape following the refining of the crystal grains can not sufficiently be attained; conversely, in the case of >0.5%, crystallized products are largely formed to cause the deterioration in the strength of the alloy.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention is suitable as a structural material for vehicles that is used in a corrosive environment and subjected to repeated stress, such as frame materials used in motorcycles, bicycles, or automobiles. This invention relates to Af1 alloys for vehicles, particularly A6000 series alloys.

BACKGROUND ART Conventionally, A60006000 has been widely used as materials for various vehicles due to its excellent hardness and extrusion processability.

Problems to be Solved by the Invention However, if the surface is not subjected to anti-corrosion treatment, intergranular corrosion will progress due to use in a corrosive environment. Such intergranular corrosion has little effect on static strength, but when repeated stress is applied, it causes a significant reduction in service life.

This invention was made in view of the above problems, and reduces the strength of the 6000 series A4 alloy, which is used in a corrosive environment and is suitably used as an Afi alloy for vehicles that is subjected to repeated stress. The purpose of this is to suppress intergranular corrosion without causing corrosion, and to provide excellent corrosion fatigue strength.

As a means for solving the problem, the present invention suppresses intergranular corrosion by reducing the potential difference between the grain boundaries and the matrix by adding a JIS A60006000 earth element.
This is designed to change the corrosion form from intergranular corrosion to planar corrosion.

That is, the present invention provides a JIS A6000 series alloy synthesis base in which one or more rare earth elements are contained in an amount of 0.05
~0. The gist of this article is an Af1 alloy for vehicles that has excellent corrosion fatigue strength and is characterized by containing 5 wt% of C.

Since it is a synthetic base of A6000 series alloy, M
g: 0.35-1.5wt%, Si: 0.20-1
．． It is essential to contain 8vt%.

Needless to say, these Mg and Si have an effect on improving the strength of the alloy, and if they are less than the lower limit, the alloy strength will be insufficient, and if they exceed the upper limit, extrusion workability will deteriorate. Note that Fe, CuSMn, Cr, Zn, Ti, etc. may be included as unavoidable impurities as long as they do not degenerate from the A6000 series alloy synthesis.

The rare earth element that is necessary to be added is not particularly limited, but specifically, for example, YlL a S (e %
Preferred examples include P r s N d s S m and the like. This Ha group element suppresses intergranular corrosion by reducing the potential difference between the grain boundaries and the matrix, and also makes the crystal grains finer and changes the corrosion form from intergranular corrosion to planar corrosion, in other words, deep corrosion. It has the effect of dispersing corrosion in the horizontal direction and preventing it from progressing in the same direction, and from the viewpoint of this effect, in the present invention, all elements of the same group (rare earth elements) are substantially mutually can be evaluated as equivalent to Therefore, one type or two or more of them can be used in any combination, but if the total content in the alloy is less than 0.05 wt%, it is not sufficient to inhibit intergranular corrosion, and also It was not possible to achieve a sufficient change in corrosion morphology, and on the contrary, 0.5wt%
If it is contained in an excessive amount exceeding 100%, a large amount of crystallized substances will be generated, resulting in an adverse effect of reducing the strength of the alloy. Therefore, 0.05~0
．． It is necessary that the content be within the range of 5 wt%.

Effects of the Invention Since this invention is essentially made of a high-strength JISA No. 6000 series alloy, it not only has high strength suitable for structural materials for vehicles, but also has low intergranular corrosion due to the inclusion of rare earth elements. An alloy for vehicles with excellent corrosion fatigue strength, which is suitable for use as a structural material for vehicles that are subjected to repeated stress in corrosive environments, as the corrosion mode changes from intergranular corrosion to planar corrosion. can be obtained.

Example Alloys having various chemical compositions shown in Table 1 were cast, and then 56
A homogenization treatment was performed at 0° C. for 12 hours.

Next, it was extruded at 530°C into a 6m x 100mg rectangular bar, allowed to cool at a cooling rate of 40°C/min, and then extruded at 180°C.
Various alloy samples were obtained by artificial aging treatment at ℃ for 7 hours (temperature: T5).

Then, the various alloy samples mentioned above were subjected to a tensile test and a fatigue test before and after performing a one-year atmospheric exposure test, and the results are shown in Table 2, while microstructural observations of cross sections were conducted.

Note that CusMn and Cr in the above alloy are elements contained as unavoidable impurities.

[Hereinafter, blank spaces] As shown in Table 2, the alloy of the present invention was exposed to the atmosphere for 12 hours.
It can be seen that the decrease in fatigue strength after several months is significantly less than that of the comparative alloys.

In addition, as a result of microstructural observation of the cross section, the alloy of the present invention was exposed to air at 1
It was confirmed that intergranular corrosion had not progressed much even after two months, whereas it had progressed considerably in the case of the comparative alloy.

that's all

Claims (1)

[Claims] Based on JISA 6000 series alloy, one or more rare earth elements are 0.05 to 0.5
An aluminum alloy for vehicles with excellent corrosion fatigue strength, characterized by containing the aluminum in a range of wt%.