Magnesium alloy for casting and magnesium-alloy cast product

Abstract

A magnesium alloy for casting according to the present invention is characterized in that, when the entirety is taken as 100% by mass, it includes copper (Cu) in an amount of from 1% by mass or more to 5% by mass or less, calcium (Ca) in an amount of from 0.1% by mass or more to 5% by mass or less, tin (Sn) in an amount of from 0.1 or more to 3 or less by mass ratio with respect to the Ca (Sn / Ca); and the balance comprising magnesium (Mg) and inevitable impurities.By means of including Cu, Ca and Sn, crystallized substances of Mg—Ca—Sn compounds crystallize in crystalline grain boundaries between Mg crystalline grains as network shapes (three-dimensionally mesh shapes), along with Mg—Cu compounds. By means of the three-dimensionally mesh constructions, grain-boundary sliding, which becomes active especially when becoming high temperature, is suppressed, and thereby high-temperature strength and creep resistance at high temperature improve. Moreover, since Sn forms compounds with Ca preferentially, it influence less on the heat conductivity, compared with the other additive elements.

Description

TECHNICAL FIELD[0001]The present invention is one which relates to a magnesium alloy for casing, magnesium alloy which is suitable for service under high temperature.BACKGROUND ART[0002]Magnesium alloy, which is much more lightweight than aluminum alloy is, is about to come to be used widely for aircraft material, vehicle material, and the like, from the viewpoint of weight saving. However, in magnesium alloy, since the strength and heat resistance are not sufficient depending on applications, further improvement of the characteristics has been sought.[0003]For example, as a general magnesium alloy, AZ91D (ASTM code) is present, for instance. Since the heat conductivity of AZ91D is 73 W / mK approximately, when it is used in member whose service environment is high temperature, or in member that generates heat in service, the radiation of heat cannot be carried out satisfactorily, and thereby thermal deformation might occur in the member. In particular, when a magnesium alloy whose he...

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Benefits of technology

[0007]As a result of wholehearted studies, the present inventors found out that it is possible to improve the creep resistance of magnesium alloy at high temperature by adding tin along with copper and calcium as another alloying element of the magnesium alloy, without ever affecting the heat conductivity adversely, and then arrived at completing the present invention based on this.

[0013]Since the magnesium alloy for casting according to the present invention includes Cu, Ca and Sn, crystallized substances of Mg—Ca—Sn compounds crystallize in crystalline grain boundaries between Mg crystalline grains as network shapes (three-dimensionally mesh shapes), along with Mg—Cu compounds. By means of the three-dimensionally mesh constructions, grain-boundary sliding, which becomes active especially when becoming high temperature, is suppressed, and thereby high-temperature strength and creep resistance at high temperature improve. Moreover, Mg—Ca compounds are brittle comparatively; however, since strength is high in the Mg—Ca—Sn compounds in which Sn substitutes for a part of Ca of the Mg—Ca compounds, the strength of the three-dimensionally mesh constructions and eventually the strength of the magnesium alloy improve.

Problems solved by technology

However, in magnesium alloy, since the strength and heat resistance are not sufficient depending on applications, further improvement of the characteristics has been sought.

In particular, when a magnesium alloy whose heat conductivity is low is used as a magnesium alloy that is used in a cylinder head or cylinder block of internal combustion engine, the cylinder head undergoes thermal deformation, or heat dwells within the cylinder block so that the cylinder bores deform, and thereby adverse affects, such as increased friction and declined air tightness, occur.

However, there might be a case where the creep resistance at high temperature is not sufficient, depending on service conditions.

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