Method of improving the coercivity of Nd—Fe—B magnets

A method of improving coercivity of an Nd—Fe—B magnet, said method comprising the steps of:

• providing an Nd—Fe—B magnet including a first surface and a second surface disposed opposite and spaced apart from one another defining a thickness of between 0.5 mm and 10 mm;
• forming a first solidified film of at least one pure heavy rare earth element attached to the first surface of the Nd—Fe—B magnet to prevent a reduction in corrosion resistance caused by oxygen and fluorine and hydrogen;
• said step of forming the first solidified film comprising depositing a first layer of powder selected from the group consisting of Dy, Tb, an alloy of Dy and Tb, and mixtures thereof, the powder having a particle size of between 0.5 μm and 300 μm on the first surface of the Nd—Fe—B magnet under an inert atmosphere of Ar with weight proportion of the powders on the first surface of the Nd—Fe—B magnet being between 0.1% and 2% by weight based on a total weight of the magnet;
• said step of forming the first solidified film further including a step of heating the first surface of the Nd—Fe—B magnet including the first layer using lighting or laser cladding to form the first solidified film of the powder attached to the first surface of the Nd—Fe—B magnet;
• said step of forming the first solidified film further including a step of cooling the first solidified film on the first surface of the Nd—Fe—B magnet;
• then forming a second solidified film of at least one pure heavy rare earth element attached to the second surface of the Nd—Fe—B magnet to prevent a reduction in corrosion resistance caused by oxygen and fluorine and hydrogen;
• said step of forming the second solidified film comprising depositing a second layer of powder selected from the group consisting of Dy, Tb, an alloy of Dy and Tb, and mixture thereof, the powder having a particle size of between 0.5 μm and 300 μm onto the second surface of the Nd—Fe—B magnet under an inert atmosphere of Ar with weight proportion of the powders on the second surface of the Nd—Fe—B magnet being between 0.1% and 2% by weight based on the total weight of the magnet;
• said step of forming the second solidified film further including a step of heating the second surface of the Nd—Fe—B magnet including the second layer using lighting or laser cladding to form a second solidified film of the powders on the second surface of the Nd—Fe—B magnet;
• and
• subjecting the Nd—Fe—B magnet including the first solidified film and the second solidified film to a diffusion treatment in a vacuum or an inert atmosphere with the diffusion treatment being conducted at a diffusion temperature of between 800° C. and 1000° C. for a diffusion duration of between 3 hours and 72 hours;
• cooling the Nd—Fe—B magnet in the vacuum or the inert atmosphere;
• and
• subjecting the Nd—Fe—B magnet including the first solidified film and the second solidified film to an aging treatment in the vacuum or in the inert atmosphere at an aging temperature of between 450° C. and 700° C. for an aging duration of between 3 hours and 15 hours.