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The microstructures of Al alloy 6061 subjected to very-high-power ultrasonic additive manufacturing were systematically examined to understand the underlying ultrasonic welding mechanism .
 material: microstructures; material: Al alloy; manufacturing process: ultrasonic additive manufacturing; manufacturing process: ultrasonic welding; concept or principle: mechanism
Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: manufacturing standard, machanical property, manufacturing process, material, engineering feature, process parameter, machine or equipment, application, process characterization, enabling technology, biomedical, concept or principle 
Text: {0} 
Answer:
 material: microstructures; material: Al alloy; manufacturing process: ultrasonic additive manufacturing; manufacturing process: ultrasonic welding; concept or principle: mechanism