Sintered Magnet Production via Low-Oxygen Strip Casting
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Low rare-earth element content in R-T-B system sintered magnets results in decreased sinterability and insufficient sintered density, which is difficult to address with existing acid treatment methods.
Innovation Solution
Controlling the formation of a discolored deposit on the surface of the starting alloy by maintaining a low oxygen partial pressure during strip casting and mechanically removing excess deposits, ensuring the area ratio of the discolored deposit is 1.5% or less, to improve sinterability and achieve higher sintered density.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If low rare-earth element content is used in R-T-B system sintered magnets, then magnetic properties are improved, but sinterability decreases and sintered density becomes insufficient
Solution Approach 1:
The oxide film is removed from the starting alloy surface before sintering through acid treatment or mechanical polishing. This preliminary action prevents oxidation during sintering, enabling low-R compositions to achieve sufficient sintered density while maintaining improved magnetic properties
Solution Approach 2:
The invention changes the chemical composition parameters by adjusting rare-earth element content to low levels (R: 27-31 wt%) while compensating with transition metal elements (Co: 3-7 wt%, Fe: balance). This parameter change improves magnetic properties while the accompanying surface treatment ensures adequate sinterability
2Productivity
If acid treatment is applied to remove oxide film from starting alloy surface, then hydrogen absorption efficiency is improved, but discolored deposit cannot be removed and sinterability remains decreased
Solution Approach 1:
The invention combines acid treatment with mechanical polishing to simultaneously achieve hydrogen absorption efficiency improvement and discolored deposit removal. This merged approach addresses both the oxide film issue and the discolored deposit issue that plague low-R composition sintering
Solution Approach 2:
The invention extracts or removes the discolored deposit from the starting alloy surface through mechanical polishing in addition to acid treatment. This extraction of the harmful deposit eliminates the barrier to sintering that prevents low-R compositions from achieving adequate density
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The method effectively enhances sinterability and secures sufficient sintered density, particularly for low-R compositions, by reducing the area ratio of the discolored deposit and minimizing oxygen content, leading to improved magnetic properties.
Implementation Method 1
hydrogen absorption time including that for activation treatment, crushing time and crushability in the presence of hydrogen
Implementation Method 2
an oxide film and/or slug is formed on the contact surface on the roll even when it is melted and solidified in an Ar gas atmosphere
Implementation Method 3
the compact is sintered
Data Source
AI summary
The present invention provides a method for producing a sintered magnet, which can have a sufficient sintered density even when the magnet has a low-R composition. The method is for producing a sintered magnet comprising R (R: one or more rare-earth elements), T (T: one or more transition metal elements essentially comprising Fe, or Fe and Co) and B (boron) as the main components, wherein a starting alloy prepared by strip casting is pulverized to a given particle size to form a fine powder, where the starting alloy comprises discolored deposit 1 on the surface and the area ratio of the discolored deposit 1 is 1.5% or less, the resulting fine powder is compacted in a magnetic field to prepare a compact, and the compact is sintered.