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Addition of about 2 % silicon to the copper-aluminum alloy helps to increase the hardness by 0.5–1 times .
 material: silicon; material: alloy; machanical property: hardness
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: silicon; material: alloy; machanical property: hardness