Aluminum alloy diecast, diecast unit and method for producing same

An aluminum alloy diecast made of an aluminum alloy comprising 7.5% to 11.5% of Si, 0.1% to 0.6% of Mg, 0.2% to 0.9% of Mn, 0.2% or less of Ti and 0.1% or less of Sr in a mass ratio and a remainder made of Al and inevitable impurities, the aluminum alloy diecast comprising:

• a part to be press-fitted having a press-fitted front surface onto which a joining member is press-fitted and a press-fitted back surface located at an opposition side of the press-fitted front surface;
• and
• a main body part having a main body front surface connected to an edge of the press-fitted front surface and a main body back surface connected to an edge of the press-fitted back surface and integrally formed with the part to be press-fitted, wherein
• an average roundness of crystals other than a primary crystal of Al in the part to be press-fitted in a range of 0.02 mm to 0.5 mm in a depth from the press-fitted back surface is larger than an average roundness of crystals other than a primary crystal of Al in the main part in a range of 0.02 mm to 0.5 mm in a depth from the main body front surface or the main body back surface.

A diecast unit comprising a joining member fixed to an aluminum alloy diecast, the aluminum alloy diecast made of an aluminum alloy comprising 7.5% to 11.5% of Si, 0.1% to 0.6% of Mg, 0.2% to 0.9% of Mn, 0.2% or less of Ti and 0.1% or less of Sr in a mass ratio and a remainder made of Al and inevitable impurities, the aluminum alloy diecast comprising:

• a part to be press-fitted having a press-fitted front surface onto which the joining member is press-fitted and a press-fitted back surface located at an opposition side of the press-fitted front surface;
• and
• a main body part having a main body front surface connected to an edge of the press-fitted front surface and a main body back surface connected to an edge of the press-fitted back surface and integrally formed with the part to be press-fitted, wherein
• an average hardness of the part to be press-fitted obtained by averaging Rockwell hardness HRF of the press-fitted back surface is lower than an average hardness of the main body part obtained by averaging Rockwell hardness HRF of the main body front surface or the main body back surface, wherein
• the joining member is fitted in a part where a part of the press-fitted front surface is recessed and a part of the press-fitted back surface located at an opposite side to the joining member is protruded.