$3.$ Friction welding is particularly noted for its ability to join $\_$ materials, making it a valuable process in the manufacturing of $\_$ where different materials need to be joined. $($Options: dissimilar, similar, automotive components, aerospace structures$)$

$4.$ Forge welding, historically used in blacksmithing, requires the metals to be heated to a temperature where they become $\_\_\_$ but not liquid, allowing them to fuse under pressure. $($Options: plastic, solid, semi$-$solid$)$