Al-Si based alloy and alloy member made therefrom

Abstract

An Al—Si based alloy and an alloy member made of the alloy, in which when alloys produced by diecasting under high vacuum conditions are welded, weldability can be improved without increasing plate thickness of welded portions and reducing gas content in diecasting.

Description

BACKGROUND OF THE INVENTION [0001] 1. Field of the Invention [0002] The present invention relates to an Al—Si based alloy and to an alloy member made of the Al—Si based alloy, and in particular, relates to a technique for producing an Al—Si based alloy which is produced by diecasting under a high vacuum and has good weldability. [0003] 2. Related Art [0004] Until now, various techniques have been disclosed as production methods for casting by diecasting of aluminum. For example, in order to improve mechanical properties, in particular, elongation by aging only, without solution heat treatment, Japanese Unexamined Patent Application Publication No. 7-91624 discloses a production method of aluminum alloy casting including a step for forming a casting by diecasting aluminum alloy, a step for coating on the casting, and a step for heating which bakes the coating on the coated casting and aging the casting at the same time, wherein the aluminum alloy includes, by weight, Si at 7.5 to 9.5...

AI Technical Summary

Benefits of technology

[0008] The present invention was completed in view of the above circumstances, and objects of the present invention are therefore to provide an Al—Si based alloy and an alloy member made of the alloy, in which when alloys produced by diecasting under high vacuum conditions are welded, weldability can be improved without increasing plate thickness of welded portions and gas content is reduced in diecasting.

[0010] 1) FIG. 2 is a graph showing the relationship between the liquid phase rate and temperature in welding in connection with each Si content in an Al—Si based alloy. As shown in the figure, in welded metal immediately after welding, the lower the Si content, the higher the starting temperature of crystallization of the solid phase, and the viscosity of the welded metal after welding is increased with increasing of solid phase. Therefore, for example, when the Si content in the Al—Si based alloy is controlled to within 7.5 to 9.0 mass %, viscosity in melting can be sufficiently ensured, and solidifying time of the weld bead can be shortened by increasing the liquid temperature and the solid temperature. As a result, throat thickness and leg length can be sufficiently ensured by preventing flowing out of weld metal, and bubbling of microbubbles of gas due to dissolving, generating and accumulating of hydrogen gas is prevented by crystallization of solid phase and blowhole in the weld bead can also thereby be prevented from forming. Therefore, weldability can be improved.

[0011] 2) When Mu, Cr, Ti, and Sr are contained in a small amount as a improvement processing agent, the alpha phase of aluminum in solidifying the weld bead is made finer, the beta phase of Si is fine-spheroidized, and therefore, strength of the welded portion can be improved.

[0012] 3) When Mn, Cr, and Fe are contained in the Al—Si based alloy, the alloy can be prevented from adhering to and burning in the metal mold, even if molten metal temperature, casting speed, and casting pressure are increased in order to compensate for fluidity in diecasting.

[0013] 4) It is preferable that Ti not be contained as a constituent element of the alloy in order to attempt to improve toughness.

[0017] As shown in the above, according to the present invention, an Al—Si based alloy which exhibits superior weldability in diecasting under high vacuum conditions can be obtained by optimizing of contents of Si, Mg, Mn, Cu, Fe, and Sr which are constituent elements in the alloy. In welding of alloy members produced by using the alloy of the present invention, by improving the weldability, plate thickness of welded portion in the alloy members is decreased and length of weld bead is shortened, and the alloy members obtained by diecasting can be thereby made lighter. In addition, the alloy members of the present invention are preferably employed as members for various processing since toughness is high as that of conventional alloy members and weldability is also high. Furthermore, welding processes can be rationalized in welding of the alloy members of the present invention, since plate thickness can be decreased as described above, etc. Additionally, diecasting process can also be rationalized since the contained gas amount in diecasting is increased.

Problems solved by technology

However, the products made of these alloys do not exhibit superior weldability.

That is, in the case in which conventional Al—Si based alloys obtained by diecasting are welded, welded metal flows out, and sufficient weld bead dimensions such as throat thickness and leg length are not obtained.

Therefore, in either case, strength of the welded portion after welding is not sufficiently obtained.

For example, when the Si content in the alloy is large, even if diecasting is carried out under a vacuum so as to decrease the hydrogen content to 5.0 cc / 100 g, crystallization of solid phase in welded portions is delayed and bubbling of microbubbles of gas is thereby caused due to dissolving, generating and accumulating of hydrogen gas.

As a result, a blowhole is formed in the weld bead and therefore, superior strength and quality of the alloy, etc., are not obtained.

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