JP2793643B2 - Aluminum alloy for vehicles with excellent fatigue strength under corrosive environment - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is suitable as a structural material for vehicles that is used in a corrosive environment and is subjected to repeated stress, such as a frame material used for motorcycles, bicycles, or automobiles. Al alloys for vehicles used in automobiles, especially A6000 series alloys.

2. Description of the Related Art Conventionally, A6000 series alloys have been widely used as materials for various vehicles because of their excellent strength and extrusion processing method.

Problems to be solved by the invention However, when the surface is not subjected to anticorrosion treatment,
Intergranular corrosion progresses when used in a corrosive environment. Such intergranular corrosion hardly affects the static strength, but when repeated stress acts, it causes a significant reduction in the life.

The present invention has been made in view of the above problems,
No. 6000 series Al which is used in corrosive environment and is preferably used as an Al alloy for vehicles subject to repeated stress
It is an object of the present invention to suppress the intergranular corrosion without lowering the strength of the alloy, and to improve the fatigue strength.

Means for Solving the Problems Accordingly, the present invention suppresses grain boundary corrosion by adding a rare earth element to a JIS A6000 series alloy to reduce the potential difference between the grain boundary and the matrix, This is to change the form of corrosion from corrosion to sheet corrosion.

That is, the present invention is based on the A6000 series alloy, that is, Mg: 0.35-1.
Based on an Al alloy containing 5 wt% and Si: 0.20-1.8 wt%, one or more rare earth elements are 0.05 wt% or more and 0.2 wt% or more.
Characterized by being contained in a range of less than 5 wt%,
The gist of the present invention is an aluminum alloy for a vehicle having excellent fatigue strength in a corrosive environment.

Needless to say, Mg and Si are effective in improving the strength of the alloy. If both are less than the lower limit, the alloy strength becomes insufficient, and if the upper limit is exceeded, the extrudability deteriorates. In addition, if Mg and Si are within the above content range, F
e, Cu, Mn, Cr, Zn, Ti and the like may be contained as unavoidable impurities.

The rare earth element to be added is not particularly limited, but specifically, for example, Y, La, Ce, Pr, Nd,
Sm and the like can be listed as suitable. This group IIIa element
In addition to suppressing the intergranular corrosion by reducing the potential difference between the grain boundary and the matrix, the crystal grain is refined to change the form of corrosion from intergranular corrosion to planar corrosion, in other words, corrosion in the depth direction is reduced. In the present invention, all the homologous elements (rare earth elements) can be evaluated as substantially equivalent to each other in view of this effect. Things. Therefore,
One or more of these may be used in any combination, but if the total content in the alloy is less than 0.05 wt%, the effect of inhibiting intergranular corrosion is not sufficient, and the corrosion form accompanying the refinement of crystal grains is not sufficient. I ’m not able to achieve change enough,
Conversely, if the content is excessively larger than 0.5 wt%, a large amount of crystallized matter is generated, which causes a problem of lowering the strength of the alloy. Therefore,
It must be contained in the range of 0.05 wt% or more and less than 0.5 wt%.

Effect of the Invention This invention is essentially a high-strength JIS A6000 series alloy,
In other words, Mg: 0.35 to 1.5 wt%, Si: 0.20 to 1.8 wt%
Since it is made of an Al alloy, it possesses high strength suitable for structural materials for vehicles, and in addition to containing rare earth elements, suppresses intergranular corrosion and corrodes from intergranular corrosion to planar corrosion. Due to the change in the form, an Al alloy for a vehicle which is suitably used as a structural material for a vehicle which is repeatedly subjected to stress in a corrosive environment and has excellent fatigue strength in a corrosive environment can be obtained.

EXAMPLES Alloys of various chemical compositions shown in Table 1 were cast and then casted.
A homogenization treatment was performed at 0 ° C. for 12 hours.

Next, the mixture was extruded at 530 ° C. into a 6 mm × 100 mm rectangular bar, cooled at a cooling rate of 40 ° C./min, and then subjected to artificial aging treatment at 180 ° C. for 7 hours (tempering: T5). An alloy sample was obtained.

A tensile test and a fatigue test were performed on the various alloy samples before and after the one-year air exposure test, and the results are shown in Table 2, while the microstructure of the cross section was observed.

Note that Cu, Mn, and Cr in the above alloys are the original elements contained as unavoidable impurities.

As shown in Table 2, the alloys of the present invention were exposed to air.
It can be seen that the decrease in fatigue strength after a month is significantly less than that of the comparative alloy.

In addition, as a result of observation of the structure of the cross section, the alloy of the present invention was exposed to the air.
Even after 12 months, it was confirmed that intergranular corrosion had not progressed much, while that of the comparative alloy had progressed considerably.

Claims (1)

(57) [Claims] 1. A rare earth element based on an Al alloy containing 0.35 to 1.5 wt% of Mg and 0.20 to 1.8 wt% of Si.
An Al alloy for vehicles having excellent fatigue strength in a corrosive environment, characterized by containing at least 0.05% by weight or more and less than 0.5% by weight of seeds.