Microstructure and tensile properties of specimens directly machined from the practical low pressure die casting AC4Aalloy engine cylinder heads with different heat treatments（T4/T6）were analyzed.After tensile testing

defects in the fracture surfaces were observed and analyzed by scanning electron microscope（SEM）attached with energy-dispersive X-ray spectroscopy（EDX）.In addition

Weibull statistical analysis method was applied to identify the scatter of tensile strength of the parts with different aging temperatures and time.The results indicate that the silicon particles in the parts after T4 heat treatment are characterized by long acicular shapes

and the specimens at both T4and T6status belong to brittle fracture mode.The T6-175℃×4h（artificially aged for 4hat 175℃）treated alloy has a maximum Weibull modulus（32.3729）for ultimate tensile strength（UTS）

which is obviously higher than those of the other specimens

meaning the minimum scatter of the data and desirable stablity

while the characteristic tensile strength of the T6-175 ℃×4htreated alloy is slightly below that of T6-155 ℃×10htreated alloy.