Single-phase solid solution cast or wrought magnesium alloys

Abstract

The present invention relates to single-phase solid solution magnesium alloys suitable for the applications as cast or wrought. These alloys are prepared by multi-microalloying with rare earth elements (including gadolinium, yttrium, dysprosium, samarium, lanthanum, cerium, neodymium and praseodymium). Each alloy contains 0.5 to less than 5 wt. % rare earth elements with a content of 0.05-2.0% by weight. The total amount of rare earth elements is controlled below 5% by weight in order for economical considerations. The amount of grain refiner calcium or zirconium is in the range of 0.05-0.6% by weight. These alloys can be prepared by die casting, permanent casting, chill casting, semi-solid processes, continuous casting and continuous twin roll casting.

Description

FIELD OF THE INVENTION[0001]The present invention relates to cast and wrought single-phase solid solution magnesium alloys with high mechanical properties, formability and corrosion resistance.BACKGROUND[0002]Magnesium alloys have not yet been widely accepted by car manufacturers. Most of the technical barriers preventing magnesium alloys from widespread applications arise from the low ductility and toughness at low temperatures, poor corrosion and creep resistance at high temperatures. Their present commercial products are normally fabricated by high pressure die casting. The use of wrought magnesium alloys is limited because of its poor formability and corrosion resistance.[0003]It will be necessary to improve the low-temperature formability of wrought magnesium alloys in order to obtain a higher acceptance of these alloys in industry. Low ductility and low toughness are due to the intrinsically brittle nature of the hexagonal close-packed crystal structure. A further issue which ...

AI Technical Summary

Benefits of technology

[0011]The strengthening effects of rare earths in the previous magnesium alloys have been explained by two mechanisms, precipitate strengthening and solid solution strengthening. Precipitate strengthening, especially the age hardening, has been emphasised to improve the mechanical properties. Without being bound to any theory, it is believed that in alloys of the present invention, precipitate strengthening is avoided and that solid solution strengthening is the main mechanism which improves the mechanical properties in the magnesium alloys according to the present invention.

[0020]The magnesium alloys according to the present invention exhibit excellent room temperature ductility with a value of about 25%.

Problems solved by technology

Magnesium alloys have not yet been widely accepted by car manufacturers.

Most of the technical barriers preventing magnesium alloys from widespread applications arise from the low ductility and toughness at low temperatures, poor corrosion and creep resistance at high temperatures.

The use of wrought magnesium alloys is limited because of its poor formability and corrosion resistance.

Low ductility and low toughness are due to the intrinsically brittle nature of the hexagonal close-packed crystal structure.

A further issue which hinders the acceptance of wrought magnesium alloys is their poor corrosion resistance.

The alloys of magnesium-aluminium series are the most commonly used in wrought applications for their relative ease of extrusion and adequate mechanical properties, but they suffer from both a pronounced asymmetry in the yield behaviour and a relatively narrow processing window.

If selecting high temperatures more than 350° C. with high processing speeds, the eutectic phases dissolve again, leading to the occurrence of hot cracking and bad surface quality of the products.

In addition, until now, the methods for refining the as-cast microstructures of magnesium-aluminium alloys are not satisfying and not widely accepted by the industry.

However, these magnesium-zinc alloys still have very limited applications because they are susceptible to microporosity during casting.

Moreover, due to the high content of zinc, it was considered that these alloys are difficult to be welded.

However, AZ31 (Mg-2.9Al-0.8Zn) alloy exhibits some problems with recrystallisation during the hot working and has insufficient mechanical and corrosion properties.

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