en Research Paper Research Paper This study was undertaken to investigate the effects of Cu and solution heat treatment on the microstructure and hardness of cast Al-Al4Sr metal matrix composite. Different amounts of Cu (0.3, 0.5, 1, 3 and 5 wt.%) were added to the composite. Specimens were heat treated at 500 °C for 4 hours followed by water quenching. Microstructural studies were assessed by the use of optical microscope, scanning electron microscope (SEM) and x-ray diffractometry (XRD). The results showed that addition of 5 wt.% Cu reduces the length of large needle-like Al4Sr phase and refines the microstructure. In addition, the presence of Cu-intermetallics increases hardness of the composite. Cu mainly forms θ phase which segregates at the grain boundaries. Heat treatment partially dissolves Cu-intermetallics and homogenizes the distribution of θ phase in the matrix. Metal matrix composite (MMC), Microstructure, Intermetallic, Hardness, Heat treatment. 48 54 http://ijmse.iust.ac.ir/browse.php?a_code=A-10-127-63&slc_lang=en&sid=1 K. Tavighi 180031947532846002837 180031947532846002837 No School of Metallurgy and Materials Engineering, College of Engineering, University of Tehran, Tehran,Iran M. Emamy emamy@ut.ac.ir 180031947532846002838 180031947532846002838 Yes School of Metallurgy and Materials Engineering, College of Engineering, University of Tehran, Tehran,Iran A. R. Emami 180031947532846002839 180031947532846002839 No Young Researchers Club, Science and Research Branch, Islamic Azad University, Tehran, Iran.