| 摘要 |
There is provided a bumper beam that is formed of a 7000 series aluminum alloy hollow extrusion, has a crushed longitudinal portion, and locally has a low-hardness region in a bumper stay joint section. A portion (portion to be heated) of end portions of the bumper beam formed of a tempered member of a heat-treatable aluminum alloy extrusion is subjected to reversion treatment, thereby forming a heat-affected zone in a bumper stay joint section. An end region (portion to be crushed) of the heated portion is subjected to cold crushing, and then the whole bumper beam is subjected to age hardening. The heated portion and a non-heat-affected zone are hardened through the age hardening, thereby forming a low-hardness region that overlaps the joint section in a portion of the heat-affected zone. |
