The Sacrificial Lamb
The title of a 1994 book proclaims the fourteen-year-old African American Emmett Till, who was brutally murdered in Mississippi for allegedly whistling at a white woman in 1955, as the sacrificial lamb of the Civil Rights Movement. As the author, Clenora Hudson-Weems explains:
In an inside jacket endorsement of my book, Emmett Till: The Sacrificial Lamb of the Civil Rights Movement, one reviewer wrote that Emmett Till was the real catalytic event that unleashed the long inhibited Black rebellion against the viciousness and brutality of White racism. It had preceded the much heralded Montgomery Bus Boycott by one hundred days.... The lynching of Till may no longer be denied as the genesis of the chronology of the Civil Rights Movement.
Till was young, perhaps too old to be called a lamb, and he was innocent of the “crime.” Yet most of all, the author suggests, his sacrifice at the hands of a white lynch mob proved to be an efficacious one, providing a focus and catalyst for an emerging movement.
One could perhaps more accurately call Till a scapegoat of racism or specifically, the racist white hypersexualization of African American men, but it would not have been nearly as powerful a book title or, as it turned out, historically apt.
While there is often considerable overlap between the meaning of sacrificial lamb and scapegoat — both of whose rhetorical power ultimately lies in the Hebrew Scriptures — a Google NGram suggests that scapegoat and its more recent usage as a verb are far more a part of modern discourse than sacrificial lamb:

Like scapegoat, sacrificial lamb usually carries a strong substitionary component, i.e., that someone or something else is to blame for something. Thus as a rhetorical device, it has an irresistible appeal to those accused or convicted of wrongdoing and their attorneys to suggest utter innocence with guilt properly residing elsewhere, and that a guilty verdict is tantamount to a “sacrifice”:
STILLWATER — The woman who was sentenced to life plus 10 years in prison Tuesday for driving her car into a crowd at the 2015 Oklahoma State University homecoming parade, killing four spectators and injuring dozens of others, was described by her attorney as a “sacrificial lamb” for the state of mental health treatment in Oklahoma.
In mitigation, Mr Muchadehama [attorney] told the court that Komichi should not be made a sacrificial lamb at the expense of others whom the court found had connived with Komichi to commit the offence. “…Komichi must not be punished for their negligence,” he said.
But Maureen McDonnell appears to have had just as much involvement in the alleged scheme as her husband did. This is not an either-or situation; if Maureen McDonnell is found guilty, it won’t be to serve as a sacrificial lamb for the governor.
It is rather rare for a legal person rather than a natural one to be termed a sacrificial lamb, but its greater rhetorical power can be seductive:
LAKEWOOD, Colo. - Calling his company a “sacrificial lamb” for problems in aerial firefighting, the owner of two planes that crashed while fighting wildfires this summer said the government tries to fight fires on the cheap, refusing to spend the money needed for a top-notch maintenance program.
In all these examples, scapegoat would have done equal service were it not for the powerful connotations of sacrificial lamb.
In other cases, where the stress lies on the sacrificial aspect, the use of scapegoat would be out of place:
The UK is in no position to support us as it will succumb to Spanish demands: we will be the sacrificial lamb on the altar of the benefit of the many in the UK.
This — not quite successful — metaphor offered by a Gibraltarian comment to a Guardian article suggests that while England and Wales voted to leave the European Union, Gibraltar will make the greater sacrifice and the rest of the UK reap the supposed benefits.
The Scapegoat
Another Guardian article discussing anti-immigrant sentiment in the UK gives an excellent definition of the scapegoat mechanism:
The poor and the vulnerable – especially those who do not share the same language or customs or religion – have always been a politically convenient scapegoat for a society’s various ills. It’s the oldest trick in the book.
It is this social aspect of scapegoating which has invited analysis from psychologists, sociologists, political scientists, philosophers, and theologians that has helped create both the verb to scapegoat and the distance between sacrificial lamb and scapegoat in the NGram.
Another reason is that scapegoat is not limited to real persons, indeed, can be used for virtually anything a writer may feel is unjustly blamed for something:
Are soft drinks a scapegoat for childhood obesity?
Headline: Sugar industry made fat the scapegoat for heart disease decades ago
AIRCRAFT manufacturer Boeing has said it has become a scapegoat for Bombardier job cuts in Belfast.
“Let’s be blunt on video games and gun violence — we will not be used as a scapegoat. The facts are very clear — no study has shown a causal relationship between playing video games and gun violence.
Any metaphorical force, much less biblical allusion, has disappeared from this usage, where the word has been semantically bleached to mean ‘unjustly blamed.’ Substituting sacrificial lamb here would border on the ridiculously hyperbolic, injecting a pathos most would consider ill-placed. And pathos is exactly the rhetorical goal of all those attorneys defending sacrificial lambs.
An earlier definition of the scapegoat mechanism comes in a 1961 film:
“Because he [Hitler] said to us: 'Lift your heads! Be proud to be German! There are devils among us. Communists, Liberals, Jews, Gypsies! Once these devils will be destroyed, your misery will be destroyed.' It was the old, old story of the sacrificial lamb.” Film: Judgment at Nuremberg (1961).
Why sacrificial lamb rather than scapegoat? 1) 1961 is too early for the entire academic discussion of scapegoating to have entered the popular imagination. 2) the Holocaust — another sacrificial ritual from the Hebrew Scriptures — is the real sacrifice of real persons no more guilty of German economic woes than any other citizen, and 3) even in the 60s the lamb had more rhetorical power than the goat.
Conclusion
Individuals, though rarely corporate entities, can be termed sacrificial lambs even when scapegoat would carry the same lexical meaning, but not the same connotations. Again, because the metaphor is still very much alive. Those who employ the expression want the reader to intuit complete innocence, the forced passivity of the victim, and the real harm resulting from the sacrifice, even death.
This would be difficult to pull off, say, with Big Sugar, a giant aeronautics firm, the video game industry — or even dietary fat — which nevertheless can be scapegoated in the minds of some writers.
The differences, then, lie more in the realm of metaphor and rhetoric than a common meaning of a person or entity suffering unjust blame which in truth — or in the pleadings of an attorney — lies elsewhere.