Bioerodible magnesium alloy microstructures for endoprostheses

A bioerodible endoprosthesis comprising:

• a bioerodible body comprising an alloy comprising at least 85 weight percent magnesium and at least one high-melting-temperature element having a melting temperature of greater than 700° C., the alloy having a microstructure comprising equiaxed magnesium-rich phase grains and high-melting-temperature intermetallic phases, the equiaxed magnesium-rich phase grains having an average grain diameter of less than or equal to 10 microns and the high-melting-temperature intermetallic phases comprising at least 20 weight percent of the at least one high-melting-temperature elements and having an average longest dimension of 3 microns or less;
• wherein the bioerodible body is created by performing at least one high-strain process on an ingot or a billet at a temperature from 250 degrees C. to 400 degrees C. and an intermediate annealing step at a temperature from 150 degrees C. to 250 degrees C. to form the microstructure comprising the equiaxed magnesium-rich phase grains and the high-melting-temperature intermetallic phases;
• and
• wherein the alloy of the bioerodible body is formed by rapid solidifying, prior to performing the at least one high-strain process on an ingot or a billet, by cooling the alloy to a temperature of 650 degrees C. or less at a rate of at least 3.0 degrees C. per second to form a cast alloy.