Aluminum Powder Passivation via Nitrogen Atomization
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Solution Overview
Problem
Aluminum-containing powders used in additive layer manufacturing (ALM) face challenges due to contamination with moisture, leading to hydrogen pores and porosity issues, especially when reused, as the aluminum oxide layer reacts with water to form hydrogen-containing pores, which are difficult to prevent even under vacuum conditions.
Innovation Solution
The production of aluminum-containing powders with a passivated surface involves atomizing a melt using an atomizing gas comprising 50% to 100% molecular nitrogen and noble gases, suppressing the formation of aluminum oxide and promoting a thin, inert aluminum nitride layer that inhibits oxidation and hydrolysis, thereby preventing water absorption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Weight of moving object
If aluminum-containing powder is used in additive layer manufacturing, then low density and good manufacturability are achieved, but moisture contamination leads to hydrogen pores and porosity
Solution Approach 1:
The patent applies inert atmosphere by conducting the atomization process in a protective gas environment (argon or nitrogen) to prevent oxidation of aluminum powder during production. Additionally, the powder is stored and processed in controlled atmospheres with low oxygen and moisture content to prevent hydrolysis reactions that would generate hydrogen pores, thus maintaining both low density and high reliability
Solution Approach 2:
The patent implements preliminary action by pre-drying the aluminum-containing powder before use in additive layer manufacturing. The powder is subjected to drying treatments (e.g., heating to 100-200°C for several hours) to remove adsorbed moisture before processing, and pre-heating the build platform to prevent moisture absorption during manufacturing, thereby preventing hydrogen pore formation
2Object-affected harmful factors
If aluminum powder is atomized with traditional inert gases, then oxidation is prevented, but water absorption still occurs leading to hydrogen pores
Solution Approach 1:
The patent applies parameter changes by controlling the moisture content and oxygen partial pressure in the protective atmosphere to extremely low levels (dew point below -40°C). The atomization process parameters are optimized to produce powder with controlled surface characteristics that minimize moisture adsorption. Storage and processing temperatures are also controlled to prevent condensation and hydrolysis reactions
3Duration of action of stationary object
If aluminum powder is stored for long periods, then supply stability is improved, but moisture contamination increases leading to porosity
Solution Approach 1:
The patent implements long-term storage stability by storing aluminum-containing powder in sealed containers filled with dry inert gas (argon or nitrogen) with controlled moisture content. The storage environment maintains low oxygen and moisture levels to prevent oxidation and hydrolysis reactions during extended storage periods, allowing the powder to maintain its properties without significant porosity development
Solution Approach 2:
The patent maintains continuous protection of the powder by keeping it in a controlled atmosphere environment throughout storage, handling, and processing. The protective atmosphere is continuously maintained with controlled humidity and oxygen levels, and the powder is kept in sealed containers until use, ensuring uninterrupted protection against moisture and oxidation
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 resulting powder remains free from hydrogen-containing pores even after multiple uses and long-term storage, enabling the production of pore-free components with excellent material properties and extended usability without significant contamination.
Implementation Method 1
a melt of the aluminum alloy is atomized with the aid of an atomizing gas consisting of 50% by volume up to 100% by volume of molecular nitrogen and 50% by volume to 0% by volume of one or more noble gases
Implementation Method 2
suppressing the formation of aluminum oxide and promoting a thin, inert aluminum nitride layer that inhibits oxidation and hydrolysis
Implementation Method 3
promoting a thin, inert aluminum nitride layer that inhibits oxidation and hydrolysis
Implementation Method 4
a thin, inert aluminum nitride layer that inhibits oxidation and hydrolysis, thereby preventing water absorption
Data Source
Figure 1~2
Figure 3~4
AI summary
A process for producing and conditioning a powder of aluminum or an aluminum alloy with a passivated surface is characterized in that a melt of aluminum or the aluminum alloy is atomized into a powder in an atomization system using an atomizing gas comprising approximately 1 vol.% to 100 vol.% molecular nitrogen and approximately 99 vol.% to 0 vol.% of one or more noble gases, with the specific objective that the powder produced thereby enables a more efficient (more cost-effective because it is reusable) and defect-free (better strength and durability) aluminum material structure by means of use in an additive layer manufacturing process.